Help a guy out with his new skiving machine!

[YinTx]

So, I have a new (to me) Cobra NP-4 skiving machine.  Been skiving up miles of leather, followed proper (as far as I know) settings and sharpening procedures, but it seems I am still doing something wrong or I have something set up incorrectly.  I am skiving some black 5 oz Horween Essex leather.  It seems to go fine when I am dialing things in on scrap bits, then when I put iny s the leather that matters, I screw it up.  Any pointers would be greatly appreciated!  Not sure if you can tell from the photos, but it will skive just fine, then all of a sudden dig in and skive to the thickness of a plastic bag, if not punch a hole all the way through.  And this without changing any settings.

You can see at the top, bad skiving - super thin, and cut through.  On the right, a decent 0.9mm skive.

 

Here is a closeup of the bad skive:

And finally, good skive on the bottom progressing to bad, then wreck my leather skive on the top.

 

[Matt S]

9 hours ago, YinTx said:

So, I have a new (to me) Cobra NP-4 skiving machine.  ...It seems to go fine when I am dialing things in on scrap bits, then when I put iny s the leather that matters, I screw it up.

I find that's SOP for most leather machines ;-) I'm sure that most have a scrap-detector hidden somewhere in the castings...

My bell-skiver is a rather old/worn in, and it's the only one I've put any decent amount of miles on so my experience is rather limited. Take that as you will. I'm sure that more widely experienced operators will be along in due course. I know that @RockyAussie has a lot of experience with them.

Things to check for as you're running the machine, in no particular order, I have found might cause or contribute to this issue:

• Scrap buildup on and around the knife and feedwheel
• Incorrect setting of the feedwheel pressure spring (too light or heavy -- experiment)
• Inconsistent feedwheel height or angle (binding of the joint, scrap/detritus buildup under the assembly or screw walkout due to not being locked down)
• Incorrect or inconsistent presser foot pressure (are you returning the lifter fully to the stop position each time?)
• Slop or other undesired movement in any part of the presser foot assembly (remembering to check any moving parts you may have in your presser foot)
• Inconsistent knife edge position for any reason (slop in the bearing, loose adjustment screw, heavy grinding etc.)

I was shown a lot of tips and tricks from the old boy from whom I bought my machine, but have found a lot of wisdom in Checaflo's videos on skiving machines. He looks primarily from a car upholsterer's PoV but most of the information is useful to most trades that use a bell-skiver, and I think they're all interesting.

 

 

 

[Sonydaze]

One thing I did to my machine that helped ease of feed as well as consistency was to polish the presser foot where the leather slides on it.  Mine is shiny like a mirror!  Stretchy leathers can both bunch and thin if there is too much friction.

Distance from the presser foot to the edge of the drum is critical, it has to be very close.  If you have to move the drum very much closer, a longer sharpening is needed to get the bevel correct. Take a sharpie and coat the cutting edge to see what the grinding is doing.

[keithski122]

I've found this website that in the last few days released a training video for skiving machines.I haven't watched it myself but probably will when I have time to watch it.Having not seen yet it I don't know if it will be useful or not.

https://www.leathercraftmasterclass.com/

[YinTx]

9 hours ago, Matt S said:

but have found a lot of wisdom in Checaflo's videos on skiving machines.

This is what I used to set it up originally, as it was all out of whack.

I'll go through your other tips to see if I can get any improvements also, thank you for those.

4 hours ago, Sonydaze said:

One thing I did to my machine that helped ease of feed as well as consistency was to polish the presser foot where the leather slides on it.  Mine is shiny like a mirror!  Stretchy leathers can both bunch and thin if there is too much friction.

Distance from the presser foot to the edge of the drum is critical, it has to be very close.  If you have to move the drum very much closer, a longer sharpening is needed to get the bevel correct. Take a sharpie and coat the cutting edge to see what the grinding is doing.

Presser feet look shiny, but I don't have anything to reference.  Was looking for a roller foot earlier, hoping that would help things a bit...used a sharpie to run the bevel just before these photos were taken, and used the rod stone to lose the burr on the inside at the end of the run.  Seemed ok...

More leather shredding in my future this evening I think...

YinTx

9 hours ago, Matt S said:

I find that's SOP for most leather machines ;-) I'm sure that most have a scrap-detector hidden somewhere in the castings...

Meant to mention the truth behind this.  It is clear my sewing machines both have one.  scrap runs fine, and the real deal skips stitches, pulls up knots, runs crooked lines, etc.

YinTx

[koreric75]

32 minutes ago, YinTx said:

This is what I used to set it up originally, as it was all out of whack.

I'll go through your other tips to see if I can get any improvements also, thank you for those.

Presser feet look shiny, but I don't have anything to reference.  Was looking for a roller foot earlier, hoping that would help things a bit...used a sharpie to run the bevel just before these photos were taken, and used the rod stone to lose the burr on the inside at the end of the run.  Seemed ok...

More leather shredding in my future this evening I think...

YinTx

Meant to mention the truth behind this.  It is clear my sewing machines both have one.  scrap runs fine, and the real deal skips stitches, pulls up knots, runs crooked lines, etc.

YinTx

I went through almost an entire bobbin a couple days ago testing the adler out for some belt stitching...seemed to be irregular some stitches great then others knots on top?  Finally after messing with tension etc i felt i had it dialed in so of course change the bobbin so i don't get halfway through the belt...then found that i had forgot to pull the thread in between the spring tension on the bobbin case......sooo started over with a new bobbin, fresh scrap and a humble attitude....lol

[RockyAussie]

I am a little afraid to give much advise without seeing some close ups of your settings and ideally a video of how it performs. Sometimes it is the operator sometimes the settings and sometimes its just a pig of a leather. Your original pics number 3 on the leather, show some coloured marking going through and that may be a sign that it not a well tanned leather. Some leathers will blunt your knife incredibly quickly and are almost like they have sand in them and some are like butter and you can go for hours without any need to sharpen the blade. IF all the settings are correct.....the best tip I have is after you have given a good sharpen and dressing and light sharpen again, cut a few strips of leather that skives nicely and run it through VERY slowly a few times. This acts to remove the slightly rough edge on the blade in the same way as stropping a knife. After a couple of feet have been run through it should be smooth as and will help to stop the edge deflecting up or down. Hard to see but if it deflects up even slightly it will take a deeper bite and if it deflects down then the opposite will happen. Notice in your photo 3 the top skive has gone rough and shows that the blade now has very small nicks in it. That is what you need to not have happen. If that leather continuously does this then it probably is not suitable. I would like to finish by adding that I don't like skiving machines without extraction suckers much and for any of you in the USA I would recommend you consider this one I found recently   http://www.techsew.com/machinery/techsew-sk-4-leather-skiving-machine-with-vacuum-suction-device.html

Having had a skiver once without an extractor I can assure you that the amount of times that the leather gets stuck to the feed wheel and ruins your work will be cut down to almost never. Once I went to the extractor versions I vowed to never ever have another one without extraction. I wont use them without a roller foot either. I'm not clever enough to make them other things work reliably any good. This is one of a few videos I did on skiving if you haven't seen it yet. Pretty sure I could not do it without a roller foot.

 

[YinTx]

Spent some time with it last night, shredded a box of crappy leather until it was running smooth.  Put in a nice piece of leather and the "good leather" sensor activated, allowing it to cut too deep right away.

 Gah.  anyhow, 90% improvement in my success using the machine.  

I took a look around without making any adjustments, and noted that the bell was jammed up with leather bits.  I cleared it out, removed the jicky catch bin, and allowed the leather bits to fall unceremoniously on my feet as I worked.  Per @RockyAussie's comment regarding clearing the machine of leather cuttings.  I think this had the single most impactful result improving my outcomes.

View of leather build up:

I also ran a sharpie again, and just touched the wheel to the stone.  It evenly removed the marker as shown, so unless someone thinks this is not what I should be seeing, I imagine it is not the issue...

sharpie...

Post sharpie and stone:

Clearance Settings views:

 

Thanks for all the help and tips so far.  Please let me know if there is another view that would assist in troubleshooting how I have things set up or how I am using the machine.

YinTx

[keithski122]

I've found that with long skiving runs the waste drops out on its own, if doing short runs it stays in grips the wheel and comes back up to the top again.

[Matt S]

Yeah scrap buildup around and inside the knife is a bugger. I don't know if it's just cos of the heavy cuts I take or if it's cos I run the knife at top speed but mine seems to clear itself pretty well most of the time. Brian/Rocky Aussie showed how 

[jimi]

Hi Yintx, wow that is a lot of scrap in there!! do you have a scrap ejector on the inside of the bell knife?? it should be normally 15 mm from the edge of the knife. Looking at the pictures the settings all look ok to me ( but i am no expert) I usually finish grinding the knife with the emery feed wheel on the inside with just a slight touch. have you checked the spring pressure on the feed wheel? for level cuts or splitting the spring that tilts the roller (the one in your first picture)should be stronger than the spring that dips the whole roller ( the spring at the back with the plate with notches) and vice versa for bevel cuts.

[YinTx]

4 hours ago, keithski122 said:

I've found that with long skiving runs the waste drops out on its own, if doing short runs it stays in grips the wheel and comes back up to the top again.

I've noted that as well.  In the case of the photo, it was all jammed up in there.

4 hours ago, Matt S said:

Yeah scrap buildup around and inside the knife is a bugger. I don't know if it's just cos of the heavy cuts I take or if it's cos I run the knife at top speed but mine seems to clear itself pretty well most of the time. Brian/Rocky Aussie showed how 

Yep, vacuum excavator is next in the works I suppose.

3 hours ago, jimi said:

ave you checked the spring pressure on the feed wheel? for level cuts or splitting the spring that tilts the roller (the one in your first picture)should be stronger than the spring that dips the whole roller ( the spring at the back with the plate with notches) and vice versa for bevel cuts.

I had no idea.  And I don't really know which one is set with more tension that which, so next time I get back to it I'll check for sure.  I'll have to print out these tips and put them with the machine until I get em all memorized!

YinTx

[RockyAussie]

3 hours ago, jimi said:

Hi Yintx, wow that is a lot of scrap in there!! do you have a scrap ejector on the inside of the bell knife?? it should be normally 15 mm from the edge of the knife.

In case you don't have one the scrap ejector @jimi is refering to is a brass bell that fits snugly inside of the bell and helps to prevent some of the leather from staying in there. Do you have it in there? Other than that I think the sharpening on your blade looks like it is to aggressive and should not be showing quite that amount of scratching. If I have taken out some sizeable nicks it would have that appearance but I come back again with a lighter touch pressure on the sharpening stone for a bit than proceed to do the stropping step. What you have there looks like a little saw and it would be easy to get a deflection on the blade particularly upward. There is way too much leather scrap sticking to your feed stone as well and that will need to be brushed off. Another thing I notice is that the guide stop looks very pointed at the front and I would suggest grinding it a bit flatter at the front in order that the leather might not be pulled into it too much and cause a possible bunching that may create bad skiving. Those pointy ones are mostly for shoe upper work and the like where you need top get around extreme curves and such. The fence/guide I mostly use has a flat about 2 1/2" long and if doing long straps you can box it in with a flat magnet as well.Then you can just hold it and let it go. Lastly and after giving it all a clean check, back your bell back a 1/2mm or so and see if it goes any smoother. I do that when doing thicker leathers normally though. Another thing when starting a skive take a little slice off the corner first by holding it 1/2 way in the go around the job in an anticlockwise action so that each new start is not on the thick. That will help not get chop out holes if you are careful when you start the feed each time.

[YinTx]

1 hour ago, RockyAussie said:

In case you don't have one the scrap ejector @jimi is refering to is a brass bell that fits snugly inside of the bell and helps to prevent some of the leather from staying in there. Do you have it in there?

Yes, there is a scrap ejector.  The plugging was clearly operator error, the jicky little bin under it was full and that stuff had no where to go but up.  I removed the bin and let er fall to the floor.  The ejector has a better chance of doing it's job for now...

1 hour ago, RockyAussie said:

I think the sharpening on your blade looks like it is to aggressive and should not be showing quite that amount of scratching.

The first day I had it, the bell was about 1/2" back from the presser foot, and when I moved it forward, the stone beveled an angle that was no where near the cutting edge, so it had to get re-profiled.  I tried to follow up with a really light touch, but it has always had that pattern on the bevel.  I thought maybe that was the way it should be since I've never seen one up close until this one.  I felt it was a bit harsh myself, but kinda didn't know for sure.  Even the light touch with the stone leaves these marks.  Do I need to find a different stone?

 

1 hour ago, RockyAussie said:

too much leather scrap sticking to your feed stone as well

It seems to grab on to whatever leather I am using like glue right away.  I'll get a brass brush and see if it'll clean up.. but if it keeps up past performance, it'll get gummed up fast.  Do I need to replace it with something that won't?

1 hour ago, RockyAussie said:

guide stop looks very pointed

my hunches confirmed again.  I think this thing can be spun around for a less pointed approach, I'll give it a try.

1 hour ago, RockyAussie said:

back your bell back a 1/2mm or so and see if it goes any smoother. I do that when doing thicker leathers normally though. Another thing when starting a skive take a little slice off the corner first by holding it 1/2 way in the go around the job in an anticlockwise action so that each new start is not on the thick. That will help not get chop out holes if you are careful when you start the feed each time.

I'll give this a whirl.  I can't wait to get this thing dialed in and my skill up on it, I think it'll open a whole new world for me...

YinTx

[RockyAussie]

1 hour ago, YinTx said:

Yes, there is a scrap ejector.  The plugging was clearly operator error, the jicky little bin under it was full and that stuff had no where to go but up.  I removed the bin and let er fall to the floor.  The ejector has a better chance of doing it's job for now...

The first day I had it, the bell was about 1/2" back from the presser foot, and when I moved it forward, the stone beveled an angle that was no where near the cutting edge, so it had to get re-profiled.  I tried to follow up with a really light touch, but it has always had that pattern on the bevel.  I thought maybe that was the way it should be since I've never seen one up close until this one.  I felt it was a bit harsh myself, but kinda didn't know for sure.  Even the light touch with the stone leaves these marks.  Do I need to find a different stone? A finer stone is often better https://campbell-randall.com/product/fav-400ro1-pink-emery-grindstone-non-porous-175-mm-bore-italy

I use a similar same brand one though it is 400SB not 400R01

It seems to grab on to whatever leather I am using like glue right away.  I'll get a brass brush and see if it'll clean up.. but if it keeps up past performance, it'll get gummed up fast.  Do I need to replace it with something that won't?I think so, a medium stone is best and I think yours may be coarse. See if you can check on that first. All that leather sticking is normally a sign that the leather is not feeding through and you are spinning your wheels so to speak. A rough wheel would give more grip but generally a better answer is a sharper blade and  maybe  better settings. If it is from 2mm+ thick leather or hard leather than a double skive is sometimes the answer. Ist skive at about 1/2 the desired thickness. Sometimes its just the bell needs to be a bit further back. https://campbell-randall.com/product/fav-801-2-50mm-emery-feeding-roller-2-medium-grit-italy

my hunches confirmed again.  I think this thing can be spun around for a less pointed approach, I'll give it a try. OR - https://campbell-randall.com/product/fav-1244-straight-edge-guide-p1657l

I'll give this a whirl.  I can't wait to get this thing dialed in and my skill up on it, I think it'll open a whole new world for me... OR -

YinTx

 

[alexitbe]

Could there be a burr left after grinding which just needs removing?

Alex

[YinTx]

Thanks @RockyAussie for more pointers, I've bookmarked the goods.

However, perhaps the plot thickens.  Here is what I came across this evening.  I noted that the feedroller was constantly pulling up leather fuzz and feeding it to the bell, as I was running it with no leather.  So I peered up underneath, and lo, jammed up under the feedroller was this nice little ball of skived leather.  I worked it out, and it promptly trapped another.  I am assuming this is not normal behavior.  How do I remedy it?  Do I need to just scrap this scraper?

 

 

19 hours ago, alexitbe said:

Could there be a burr left after grinding which just needs removing?

Alex

Entirely possible, I've tried to make sure there isn't one, but this bell thing is new to me and I'm learnin...

 

I also have proof the good leather sensor is functional on this unit.  Ran a lot of scrap in there, it skived beautifully, went to skive the good stuff, and viola, shredded.  Picked up a piece of scrap without changing a thing, skived it perfectly.  Sensor functioning.

YinTx

[RockyAussie]

1 hour ago, YinTx said:

 I worked it out, and it promptly trapped another.  I am assuming this is not normal behavior.  How do I remedy it?  Do I need to just scrap this scraper?

Oh mate i am feeling the pain from here. I dont have any of that scraper stuff on mine and I suppose that is because of the suction equipment on them. That dish shaped ejector thing at the back is about 15mm or less in and that keeps the bigger strips from going around and around. From what I can make out in your photos the scraper is a plastic wear style thing and should be adjustable to run right up against the feed stone. If it is held against the feed stone with a spring pressure it may not be adjustable in which case a smoother feed stone may be an answer.Almost any gap will work to trap the thin skived pieces so if it is adjustable I would give it a try right up lightly touching myself. Hopefully others here hopefully may have experience with this arrangement. The other thing is that if you bring the dish ejector forward you will need to bring back as well that other metal scraper as well and that should work to eject the strips better. You probably have already seen this post but in case you want to see it again this is it -

You know if I were making that style of ejector wiper thingy I would have used a shaped out bristle brush to really scrape that fluff out of the grit.

[RockyAussie]

Just another thought ....I think that plastic wiper thing will be spring pressured and with the plastic block being somewhat thick it may act as a funnel and be excellent at trapping the leather until it wears down to where there is no edge left and it is firm against the feed stone. Try having it run with the feed stone engaged until you can see no ledge. What have you got to lose?

[alexitbe]

I don't know anything about this machine, but is the scraper at the correct position and angle to the knife?  Is it possible to vary these?  I would put the scraper either just after the leather has been cut by the knife or at 6 pm on the bell knife after gravity has collected all the leather from the cut... I guess there will be an optimum angle too...

 

Have you thought of replacing the scraper with something that doesn't let things gather under it.... say something like an angled rod (like a finger stuck inside bell knife) that presses into the bell knife... It would remove the big pieces of leather, which presumable take the littler pieces with it...

 

alex

[keithski122]

Looks the same as mine.Metal scraper on the right against the knife, leather scraper spring loaded against the feed wheel.

I don't suppose you can get a pic up on how the spring for the feed wheel scraper is fixed as mine has come off and the scraper is dangling loose in the air doing nothing. Many thanks if you could.

[Mark842]

I'm curious, did you sharpen it using the supplied instruction manual as a guide (hieroglyphs and braille) or by Al Bane's video? I had similar issues sharpening by the manual. Then I found Al bane's video on YouTube and everything works great. I skive mostly 5 oz oil tanned and have found that I need to sharpen the blade every two days or so depending on work load.

 

 

[YinTx]

13 hours ago, RockyAussie said:

You know if I were making that style of ejector wiper thingy I would have used a shaped out bristle brush to really scrape that fluff out of the grit.

yeah, I would have engineered it that way too.  I know a company that makes metal wire scrapers, I may replace it with one.  This one is frustrating.  It pulls the pieces in right away as they are getting cut.  Defeats the purpose a bit, I'd think.

 

2 hours ago, keithski122 said:

as mine has come off and the scraper is dangling loose in the air doing nothing.

Probably better than trapping leather trimmings!  But I'll try to get a photo later this week if I can.  Kinda hard to get the phone up in there and all...

9 hours ago, alexitbe said:

but is the scraper at the correct position and angle to the knife? 

I think so.  I imagine it has a lot to do with the fact that the spinning bell lifts the leather towards the operator and thus the scraper, causing it to fall down.  It seems to do it's job ok, the other scraper tho leaves a lot to be desired.

12 hours ago, RockyAussie said:

Just another thought ....I think that plastic wiper thing will be spring pressured and with the plastic block being somewhat thick it may act as a funnel and be excellent at trapping the leather until it wears down to where there is no edge left and it is firm against the feed stone. Try having it run with the feed stone engaged until you can see no ledge. What have you got to lose?

I'll look closer, when I was looking at it last night I noted it was on a spring, but didn't seem to actually touch the stone.  Perhaps it is somewhere that I can't really see, like the backside, closer to the operator.  I don't hear any rubbing or anything while in operation tho...I'm just glad I am willing and able to troubleshoot this thing.  Otherwise I'd be one unhappy camper!

YinTx

[YinTx]

10 minutes ago, Mark842 said:

by Al Bane's video?

I had seen this video, and pretty much followed it. Thanks for posting it, others may find it useful.  I didn't have the issue he had with skipped sections, but the angle of the grind was off due to the bell being so far back initially.

Mr. Bane was freaking me out feeding that leather through one handed with his fingers right above the bell business end.  If that had bit into the leather there, he would have had red accents on the black.  I keep my fingers clear of that thing at all costs.

YinTx

[RockyAussie]

Do you not get any manual with this thing? I just spent ages going over the videos on skiving machines and .....mostly was horrified at the amount of misinformation out there. Why anyone that makes video's on how to set them up when they have just got  one is beyond me. These videos get thousands of views and that is a bit sad I think. I am not knocking that some may think they are helping perhaps and for that they should be commended. I saw one deler video that I think does some pretty decent video's on sewing machines but as for his skiving machine information .....IT is nothing but crap.For anyone that ever sees this post please understand that there should NEVER be an occasion for you to ever have to pull the leather through a skiver. If that feed stone or roller is not feeding it through by itself then you have unwanted friction that is distorting/stretching the leather and on finer leathers you will get a lot of inconsistency problems. If your leather is not going through smoothly as I show in this video then something is wrong -

By my standards the smoothness shown here is not even optimal but against many other video's I just looked at you'd think I might know what I am doing. My normal brass roller I made and use allows me better control than shown here. @YinTx I have to ask if it would be possible to do a short video of the machine in action? This may help to establish if you are getting anywhere closer.