jfhspike

Just in case anyone else ever needs this: it's M10 x 1.00 (i.e., extra-fine thread). Also, the threads only extend about 3/8" or 1/2" into the crankshaft.

I've got a Bernina 217. I'm trying to add a needle positioner. The adapter that is held to the crankshaft just beyond the handwheel came with two screws (One looks like M8; the other is a little smaller), one of which is supposed to fix into the threads in the end of hte crankshaft. But my Bernina appears to use an M10 screw. My problem is the thread-pitch. I've tried M10 - 1.50 and M10 - 1.25 and neither wants to go in (although the 1.25 seemed promising for about 3/4 turn or so). Does anyone know whether it's actually an M10-1.00 (which is "extra fine" in metric terms) or perhaps some custom thread. Any advice eagerly accepted. --John

Thanks, folks. I do a lot of zig-zag sewing -- thread costs less than my time, and I make enough errors that the ease of removing zig-zag stitching is of real value still. Also, zig-zag tends to not "bunch up" the cloth as much as does straight-stitch, when I'm working with few or lighter layers. For making a dodger...I'll use mostly straight stitching, and for the cloth-only parts, I'll probably use the Bernina (or Adler if I buy it); for the parts that involve strataglass, or vinyl-plus-sunbrella assemblies (e.g., handhold areas) ... well, that's a really good place for the Juki and its walking foot. I sure wish I had the Juki-with-reverse, but having picked up this one, with table!, for $60, it's hard to let it go. I'll mull over the Adler for a little longer keeping thoughts of what you've said in mind. --John

I've got a Bernina 217 that I like a lot. My sewing is mostly sails, canvas covers for boats, and things like 'dodgers' (http://www.shipshapecanvas.com/canvas_dodgers.php) which involve sewing through both thick plastic and multiple layers of Sunbrella. What's not great is that the foot pressure is (somewhat) limited, and the bobbin is small. For really substantial jobs I'll haul out a Juki 562 (with no reverse) that I picked up amazingly cheap...but it's straight-stitch only, and has no reverse. I've got a chance to get an Adler 98-2-8. It's not a walking foot, which would be nice, but otherwise looks like a beefier machine than the Bernina, and at least one place I read said that it had a really strong feed, which would be great. I'd probably sell the Bernina if I got the Adler. Any thoughts? (Availability of parts? Quality of the machine? Suitability for these kinds of tasks?) Thanks in advance.

I've got a Bernina 217 that I got from a friend who could never get it to sew right, and I'm now starting to work my way through the "adjuster's manual" to try to get it working a bit better (and doing some cleaning, oiling, etc. along the way). The manual says things like "The needle must enter the middle of the stitch hold see from front-to-back" (i.e., it should be the same distance from the "feed" side, or "operator side" as it is from the "exit side"). I understand what this means, and how to adjust it, but what I don't know is the tolerance: should I be making these distances match with feeler gauges or a micrometer depth gauge or calipers, and worrying about .001" adjustments, or is .01", which I can see with a good eyeballing, good enough? (It's pretty obvious that something is terribly wrong with at least the bobbin/hook timing adjustment, because when I set the needle to far-left, it hits the bobbin case rather than slipping down into the cutaway part the way that it's supposed to. But right now I'm at a step 1, which is the needle stitch-hole adjustments). Once again, thanks in advance for any advice you have. My new dinghy spritsail will appreciate it.

Thanks for the suggestions. The problem is sadly not the lack of hollow grind on the blades, but really a matter of angle (and the oval-head shape of the adjusting screw, which compounds the problem). I think I'll make myself one of those cutoff-mini-drivers I was describing and see how it works out...

I have a Juki 562 with a bobbin-case that's captive (i.e., you have to undo a screw or two to remove the case). That makes adjusting the lower tension a pain...except that if I move the hook to the right position, I can see the lower-tension-adjusting screws, and can reach them with a jeweler's screwdriver...at an angle, because the screwdriver has to come down into the bobbin-case area from above. And that angle makes the adjustment a pain in the neck. Does everyone in the world except me have a "sawed-off jeweler's screwidriver" for situations like this? Or is there a proper tool for this job and I just don't know about it? (I'm thinking that about 3/4" of screwdriver blade, with the back 1/4" wrapped in adhesive tape to give me something to grip...that might just about do the job, since not a lot of torque is required.) Thanks in advance for suggestions (perhaps including "You're supposed to take the case out to adjust that, you idiot!")

Thanks for the suggestions, everyone. I tried a different needle (no effect), checked for burrs (none), and then noticed that the problem only happened when I was going fast. At "half-clutch" speed, things worked fine for many many inches of stitching. I figured it HAD to be a hook/loop issue. When I looked at the hook closely, it turned out to be about .04 or 0.5" from the needle. You couldn't quite drive a truck through there, but close. I adjusted the hook position to be a good deal closer, and things now seem to be fine. I would have checked sooner, but seeing the hook/needle position is harder on this machine than my old 31-15, so I never really checked closely. D'oh!

I'm sewing 4-6 layers of cloth-backed vinyl with a Juki LU-563, V-92 thread, #18 needle, about 6 stitches to the inch. It's mostly going fine, but every 20 inches or so, I get a problem (as shown in the image below): the thread bunches up above the eye of the needle. I suspect that either (i) the hook is sometimes catching only half the thread, essentially splitting it into two strands; one breaks, the other continues to work as usual, and the broken one is bunching up, or (ii) something else is causing one strand to break -- perhaps excessive tension or something. Anyone have thoughts about what might be causing this problem, and how I might address it? I've wondered if part of the problem might be the "stickiness/slipperiness" of the vinyl, perhaps making it fail to hold the thread down enough as the needle's withdrawn to form a proper loop for the hook to grab. If that's the problem, should I try a larger needle? Smaller? Voodoo? Thanks in advance for any suggestions you might have.

Thanks. That photo looks just like what I do, although I use jeweler's screwdrivers instead of the eye-glass ones. Glad to know I'm not along. (Thanks to Stanly, too, for the "there's no right answer here" answer regarding good tension -- gives me confidence that my eyeballing is about right.)

Hi. I've got a two questions about tension adjustment. 1. I know how to adjust things so that the upper and lower tensions are about equal, so that the knot is buried in the material. But there are many ways for two things to be equal: the upper and lower tension can both be large, or both be small. Is there some rule of thumb about how much tension to put on the bobbin (and then match with the upper tension)? Clearly for light fabrics like silk, too much tension will make puckers between stitches, but I'm working mostly with sunbrella, and there's a pretty wide range of tensions that I can put in and still have things work. 2. I'm using a Juki LU-563, with a horizontal bobbin. When you change bobbins, you just lift out the bobbin, not the whole case assembly like you do on some machines. I switch back and forth among threads from V69 to V207; that requires adjusting the bobbin tension, which seems to be placed so that no reasonable screwdriver can get to it comfortably. Does someone make jeweler's screwdrivers with a right-angle bend in them or something? Or does everyone else just swear at their machines like me? Thanks in advance for any advice. -John

Hi, blue99. Look really closely at what happens during stitch formation. There are two things going on. (OK, there are a million things going on, but let's concetrate on two of them). (1) The needle is plunging down through the material, pulling up a bit to form a bulge, which the "hook" is catching and wrapping over the bobbin, forming the "knot", and then rising up to pull the knot -- both the "top" and "bobbin" halves of the knot -- up into the midpoint of the material (at least if you've got things set up right). (2) The cloth is being advanced by the feed dogs, so that the knot you've just formed is now pressed between the feed dogs and the plate beneath it. That holds tension on the "already sewn" part of the two threads so that the needle/tension and bobbin/tension assemblies can get the right tension in the next knot. Imagine if part 2 happens too early -- before the needle and the up-and-down-arm that's above it have pulled the knot into the cloth, the material has already advanced. You end up with a loop of top-thread dangling below the cloth, and pinched between the foot and plate. The arm rises up but cannot pull that loop back up tight, and instead pulls more thread through the upper tension assembly. If you think about this, you'd expect the problem to be worst with long stitches. With short stitches, the previous knot isn't really all the way under the presser foot as described in item 2 above. (This is what I found on MY machine; if you don't have these symptoms, then I doubt my solution is the one to follow!) So I'd try the following: back off on the stitch length until you're making quite small stitches and see if the loops still appear on the bottom side. If not, then with small cloth-advance, you're good, but with large cloth-advance, you're getting the pinching I described. You might even want to try the small cloth advance and see whether you can adjust the tension to something reasonable in that situation. What you need to do, IN THIS CASE ONLY -- i.e., only if the "small stitches" situation doesn't make loops and lets you use more reasonable tension, but long stitches make you get loops -- is to adjust the timing of the feed-advance vs the needle/hook operation. How do you do that? None of the manuals I found described that, so I'll make an attempt here. Look at page 4 of http://parts.singerco.com/IPinstManuals/31-20.pdf; there's a cover plate marked "F" in Figure 3. If you look behind that cover plate, you'll see that the main crankshaft of the machine is visible. Two things are driven by that crankshaft at that end, and ONE of them drives the feed-dog assembly. Look at the diagrams at http://parts.singerco.com/IPpartCharts/31-15.pdf Find the page saying 22303-1/3 at the right. There's a screw marked 446AL; if you loosen that, the feed eccentric (127152) can be rotated on the crankshaft by a few degrees, adjusting the timing of the feed. Which way do you rotate to advance or retard the feed? I have no idea. I did it by trial and error. I want to be clear here: adjusting this is what I did to make my machine work, but I'm NOT a sewing machine service person -- just an amateur kind of mechanically inclined guy. It's pretty clear to me that adjusting this eccentric too far can really screw things up, and trying to make the adjustment through that cover-plate hole isn't easy. If I were you, I'd be very certain to mark the initial position of the eccentric so that you can put it back to its former state, and try adjusting it by only quite small amounts to see if you can improve matters. The fact that adjusting this eccentric is not included in the general manuals suggests to me, at least, that you're messing with the Dark Arts, and are more likely to screw things up than fix them. I'd never have done it to mine if it weren't essentially a machine that I could afford to destroy (I only paid $50 for it). Anyhow, with that caveat, and with a clear understanding of what I've written above, you could try what I'd described, and it if works for you, let us know. Or you could take the safer route and have a professional adjust it for you. By the way, when you adjust that screw, make sure to use a screwdriver that fits really well -- wide enough for the slot, thick enough to fill the slot but not so thick that it won't go in --- and make sure to snug it up decently when you're done. You'd hate to have the feed adjust itself during your later sewing.

Thanks for the suggestion, Merlyn616. As it turned out, it was a top-end timing problem for me, but there's probably someday going to be someone else reading this thread of postings for whom your answer is exactly what's needed. I'll keep in mind the idea of adjusting the tension rotation as a possible fix for future problems. --J

Exactly -- it was that comment that got me thinking, and I looked around and couldn't find any information about how to adjust this "top end timing," so I went with the "maybe it should work like other machines" approach. Thanks again for steering me right. -John

SUCCESS! After careful side-by-side comparison of the 31-15 and my Pfaff 140, I decided that the timing of the feed dogs really WAS wrong on the Singer. Basically, the material was done feeding by the time the thread-take-up lever reached the top. That meant that the stitch I was trying to tighten was already "buried" under the presser-foot, and things just weren't working. By contrast, on the Pfaff the feed dogs were at top dead center just about the time the take-up lever reached its top position. So, after carefully marking the current position of the feed-dog cam (which was pretty easy: the grease on the main shaft was a perfect medium in which to draw a "line" with a small awl), I went ahead and retarded the feed by about 30-40 degrees. Result? Perfection! The stitches look like real stitches, I can reduce the tension by about 2 turns from where it had been, and I can even tighten up the bobbin tension a little without any adverse effects. And when I stitch that sailcloth, it looks like a sailmaker did it rather than a bozo Part of my reason for being willing to mess with the feed timing is that it was clear that it had been messed with relatively recently (less accumulated grease there than on other nearby areas of the machine, and a slightly bunged-up screw-slot was a further clue. I would not, in general, recommend that anyone with a machine that's worth real $$$ try this. I only did it because my machine cost just $50, and I figured I didn't have much to lose. Thanks again to everyone for helping talk me through this. You guys helped me figure out that if I just reasoned about it hard enough, I'd get somewhere. --John

Sorry -- I wasn't clear. I meant that I cranked the PRESSURE down, by screwing counterclockwise. Anyhow, here are the results of tonight's experiments: 1. I looked around for another foot, and found the only other one in the drawer appears to be a 1/4" welting foot (I'm only guessing from the shape, of course). The key thing is that there's this big "tunnel" down the middle, hence nothing to pinch the upper thread. Result: Joy! Beautiful stitches. Upper tension something like 3 turns away from "cranked all the way down". 2. Swapped back to regular foot...no joy. Loops prolapsing from the bottom of the material. 3. Changed back to regular needle plate and feed dog (and then spent time messing with adjusting the feed-dog position, because it has to be reset for the different dogs). Set up machine with regular presser foot. Took a few stitches (and inch or two) that looked OK for knot-position, but with the bobbin thread kind of slack. Tried again and...ran out of bobbin thread. 4. Wound a new bobbin. Found that with regular foot and regular plate and dog, at 16 stitches per inch, things look OK. By the time I'm down to 12 per inch, I get loops. Overall: the test with the welting foot convinces me that the upper thread's getting pinched under the foot, and even very modest presser-foot pressure is enough to cause a problem. Once the stitch-length is great enough with the regular foot, the trapping of the upper thread under the foot starts. I think that when the stitch-length is too great, the workpiece moves, and it moves back BEYOND the slot in the presser foot -- maybe 1mm beyond. So maybe I need a presser-foot with a deeper slot between the two toes, or need to go with a shorter stitch-length, or...who knows. But with all your help, I feel as if I'm definitely on the right track now. Thanks again, everyone. --John PS: I just noticed that the presser foot I'm using is the most basic possible: it's a single casting, with no "ankle joint" of the kind I'm used to seeing on my Pfaff. I doubt that this is a major cause of problems, but perhaps it's worth considering.

Yep. I cranked it pretty far down, with no real improvement. But I'll try going down further before I swap the feed dogs and throat plate. I was also considering the possibility of filing a small groove in the middle of one of my spare presser-feet, just wide/deep enough to let the thread slide in it. But I'll only go that route if other things don't work first. (If I were making short stitches, this would all be no problem, I expect. But 1/10" stitches are actually pretty short for the sort of canvas work I'm doing, and after 1/10" feed, the hole is firmly buried under the presser foot. --John

Brilliant! You guys are awesome (esp. you, Wizcrafts). You pointed me towards the problem, which I should have seen about 10 posts ago. My thought was "if there's so much tension that it's pulling the piece back, SURELY that's enough to pull the knot up through the material. UNLESS the tension on the upper thread is coming from the pinch between the foot and the material and the throat-plate..." So I tried removing the throat-plate and sewing a couple of inches. The result? Not very pretty stitches, but with the knots on TOP (as you'd expect with too-high top tension). In fact, the throat-plate I removed was my new one -- a "heavy duty" model that was needed to use a heavy duty feed dog, which seemed like a good idea for working on big canvas (think of a cover for a 35 foot boat -- it weighs about 100 lbs!). That heavy duty plate actually is THICKER than the normal one -- perhaps 1.5mm thicker -- which probably increases the effective presser-foot pressure (and means that the knot would have to get pulled up about 1.5mm more, too!); it probably all conspires to just screw things up (to use the technical term). I'm betting that a swap back to the old dogs and plate may resolve all my problems; we'll have to see this evening when I'm back from work. But I'm definitely on the right track now. Thanks! -John

Thanks for the ideas, catskin. I think you're partly on to something. The material isn't lifting, but the shiny coated dacron sailcloth IS very slippery. And when the take-up lever is at the very top, tugging on both the upper thread at the workpiece and the thread coming through the tension disks, there's a moment when it actually manages to pull the workpiece BACK towards me a tiny bit. That sure suggests that there's plenty of tension there. What I can't figure out is why it's not managing to pull the bobbin thread UP as it should. Unfortunately, even when I hold the work and move it along with the feed dogs so that the backsliding DOESn't happen, I still get the little loops. I can confirm that the material isn't lifting any more than the sunbrella was lifting -- probably less -- and that the foot tension is quite high -- higher than on my Pfaff 140, for instance, by a substantial amount. Boy, I'm getting to know this process WAY better than I ever intended to. --John

OK. The first sequence shows the thread path. Pardon my cone-holder; the one in the real sewing table is a little more sophisticated. I put some brown sunbrella behind things to make the thread path easier to read. Second sequence shows 8 equal steps in the operation of the machine, seen from the end. In about step 5, you can see the top-thread coming off the bobbin that it's just passed around. Third sequence shows the tension spring and thread-take-up-lever in a similar 8-step sequence. Sorry about the bright highlight; I was trying to get things well-lit for this sequence. --John

Oooh! I really liked this idea, and ran downstairs to test it...but alas, no joy: the top thread slides around the bobbin smooth as can be. (Sigh). --John

I'll try to get some light on the workbench, and pry the digital camera from my son's hands, and send in photos. To answer your question: yes, #18 needle, V-69 dabond thread, both top and bottom. As for sending to Toledo...I've only got about $90 in this machine so far; it might make more sense to give up, and call that the price of learning than to double or triple my costs by sending the thing to Toledo. I might look around for someone more local (Boston, Providence RI) and go ahead and pay for an honest tune-up ... if there actually is anyone local and competent to do the job. Photos later tonight if possible. --John

Wow! It's really terrific having experts like you willing to answer my questions. To answer YOUR question: I've replaced the race already, so there's no real play in the shuttle that I can detect. Here's the current status: First, I'm not sure I'm making progress, but I'm learning a lot. Second, I'm starting to get blisters on my fingers from turning over the handwheel while the machine's on my workbench rather than in its table. Things I've messed with so far: Just after the take-up spring at the tension disks, the thread passes under a hook (part number 20060, which one manual calls the "thread regulator") and then up to the "thread take up lever" part 12408). That thread-regulator was slightly bent away from the disks, so when the thread-arm reached the top to do it's "tug" on the thread, that regulator was flexing a bit. I straightened it out so that when its screw was tightened, the regulator was pressing against the head-casting and therefore the hook part was essentially immobile. I realized that the tension disks are not really tension-setters so much as tension multipliers, where the base tension is set by that little button about 4" above the disks. (In the parts-diagram I've got, that button isn't shown, but an assembly with three holes -- 52454 -- IS shown instead. I assume the button was a modern improvement or something). The thread was going over that "button" about 90 degrees, perhaps 1/16" from the outside edge of the button, but by removing and inspecting the button aseembly, I learned that it was supposed to pass almost through mid-button, so that a little spring could press a washer against it with a constant pressure. I learned how to extract the take-up spring on the tension disks and re-set it. It seems that you get to set it in units of "one full rotation of springiness". If you simply insert it and move the spring around until it goes where it's supposed to go, it seems to have about, say, 30 degrees of "spring"; the next option is 390 degrees of spring, and so on. I decided to try the 390 instead of the 30 setting, but it had no real impact on my problem. When I sew two layers of sunbrella, it works OK, but only with the tension disks tightened to the point where I'm running out of threads to screw the nut on. When I switch to the shiny dacron sailcloth, I get the "loops hanging down" thing again. (Just to be clear: when I remove a 4" workpiece, I can grab the bobbin thread and give a good tug and pull it out essentially straight -- it has no "kinks" in it from the stitching -- and the upper thread now shows as a sequence of tiny loops (1/64 - 1/32"?) hanging down from the bottom of the material. When I pull out this upper thread, it's all kinky from having the loops in it, of course.) Other things I've done to the machine: Cleaned everything I could see with alcohol and q-tips, and then oiled everything. It appears, from the kind of grunge I removed, that this machine had be used on leather in the past. Replaced the tension disks (they were a little rusted on the inside) and spring Replaced the shuttle race and its holder Replaced the needle-holding-thinghy-with-screw (the old one had been torqued by a gorilla until there was almost no slot left in the slotted screw) Switched to a heavy duty needle plate and feed dog Timed the needlebar so that I get no missed stitches Adjusted the feed-dog timing/positioning Now that I've spent another few hours on this machine, I'm beginning to grasp MOST of what's going on the sequence of operations, at least for the thread-part. The feed-dogs, which seem to be doing their thing properly, and their driving assembly -- those are still a mystery to me, which is fine. If I get it right, the sequence is something like this: Needle descends through material. At the bottom-dead-center, it starts to rise. Thread in the groove in the left half of the needle gets lifted through the cloth; thread on the right half, which is pressed between the slippery needly and the rougher material, does not, and the thread "puckers" out to the right. As this pucker forms, the shuttle-hook enters it from back to front, and pulls a loop of thread downwards and frontwards. This "loop" is provided by the thread-take-up-lever descending, which gives just enough slack to let that loop make it around the bobbin. By this time, the needle has risen out of the material The loop slips around the bobbin and the shuttle-hook retreats; the loop is pulled around the bobbin (linking it with the bobbin thread!) by the rising of the thread-take-up-lever. At about this time, the feed dogs move the material backwards one stitch-length, so that when the take-up-lever is at its highest point, the material has stopped moving. As the thread-take-up-lever gets near its highest point, the take-up spring near the tension disks starts getting tensioned; for the last little bit of take-up rise, the tension is so great that the take-up-spring is pulled down all the way, and thread runs direct from the tension-disks to the thread regulator. During the last bit of rise, there's a balancing act: the tension produced both pulls the "clasp" of the upper and bobbin threads up into the material AND eventually gets great enough to pull a bit of NEW upper thread through the disks. That new bit of thread will give us the stuff needed for the next "straight-line" part of the upper-thread in the new stitch. The process re-starts. As the needle descends, the take-up-spring maintains some tension on the upper thread, so that it lies flat on the material rather than forming a slack loop there. Once the needle-eye meets the material, there's no need for the take-up spring to act further, so it should be adjusted to be slack by this time. What I don't see is how the balancing act described in part 4 works: why if the the thread tension is great enough to pull the "lock" up into the material, doesn't it pull the lock all the way THROUGH the material? Why does it stop pulling on that part, and suddenly start pulling on the 'tension disk' side? Is the pin in the tension disk assembly (32574) riding on a cam or something and causing the disks to loosen at some critical moment? This is the one part of the sequence that I'm not getting. In a related question, it seems as if once the material has been moved by the feed-dogs, the take-up-lever applying tension has to pull the thread "around a corner" (the corner being at the presser foot), at least for long sttiches like 1/8", which is mostly what I do. If I were designing the thing (hah!), I think I'd want to have the feed-dogs act during the DOWNstroke of the needlebar, but presumably that wouldn't make it easy to adjust the amount of thread available for looping-past-the-bobbin depending on stitch-length. Am I missing something here? Any insight you might have would be much appreciated. I have one or two questions that I CAN ask coherently: The "button" -- the first thing the thread passes over after it leaves the "pins" near the handwheel -- has a spring whose tension is adjusted by how far in the button is pressed before it gets screwed into place. Any suggestions on how far in that should be? Does anyone actually put NUMBERS on things like "upper thread tension"? It'd be pretty easy to say "adjust the tension until the crossover from static to sliding friction occurs at about 4 lbs of force", but I never see this mentioned. Presumably, once everything is working, I can adjust the upper and lower tension in parallel; if I make both larger, then the stitching will be very tight, and if the material I'm using is something gauzy, it'll end up all bunched up and gathered by the too-tight tension. If I make both lower, then the two pieces of material I'm sewing will be held less tightly against each other, which is probably OK up to a point (esp. for gauzy stuff), but not what I'll want when sewing canvas. So how tight DO I want it? Just short of thread-fraying-and-breaking-during-sewing? Or something else? The thread-regulator is held in with just one screw, but that screw's in a slot, and the whole assembly can be rotated +/- 10 or 15 degrees as well. Does it matter? What would moving it up or down (which is how the slot's oriented) do to the stitch? Thanks again in advance, -John

50 years, Wizcrafts-- Thanks much to both of you. Your answers inspired me to drag out my Pfaff and watch it in slow-motion (i.e., using the handwheel) until I got a better idea of what was going on in the system. I'm still not sure I'll be able to make the Singer do what it's supposed to do, but at least it's a start! --John

Wow! Thanks for the (very) quick response. I'm pleased to say that I'm with-it enough to have checked almost all of those things. (Yay!) I don't know how to assess #5, but the spring tension seems similar to that on my Pfaff 140 and other machines I've used. For #7, the bobbin thread seems to have no problems. For instance, when I stop sewing and lift the presser foot, it's easy to move the material away from the foot to cut the two threads. For #8/9, I'm using V-69 thread, and Sailrite says "Use V-69 and a #16 or #18 needle for fabrics up to six ounces and with Sunbrella". I've got a #16 needle in the machine, and I'm sewing shiny dacron sailcloth (but only two layers -- nothing fancy!) I'll try a #18, but I was getting exectly the same behavior when I was using V-92 dacron thread and a #20 needle. It may be too much to ask, but can you explain the function of the check-spring? It's got such a small travel (perhaps 3/8"? Maybe a little more) that it's hard to see what it could be doing. And can you tell me when, in the stroke-cycle, the "clasp" or "lock" gets pulled up into the material? Is it when the needlebar is at the top of its stroke? When the "thread lever" (the thing the thread goes through after the tension disks) is at the top of its stroke? I can't really figure it out, because it's usually happening pretty fast. Thanks. -John