The cheapest motorized Chinese Cobbler?

[SmartShop]

I just signed up for an account because I have wanted to sew heavy leather and nylon strapping for a long time.

After seeing several motorized Chinese Cobbler machines, I started thinking about how I could do it cheaper and if not better, good enough.

I think I have come up with a $30 conversion (including motor).

There are a few reasons why I want to tell people about it.  First it is cheaper than anything I have seen.  Second, it will not require any machine work beside a motor mount bracket.  Lastly, it should have more torque than the other low cost conversions I have seen.

So far parts are trickling in, sadly one key $3 piece is shipping from China and that may take a while.  I guess that gives me time to tune up the manual operation.

I'm also thinking about adding an 8 position detent so I can stitch back and fourth at 45° increments and making a strap guide to keep everything aligned.

I got my cobbler "open box" for $70 so I should have mine motorized and tuned up for less than some people spend on the base machine.

Edited December 8, 2020 by SmartShop

[SmartShop]

First, a little background, I started by looking at YouTube videos because I want to see it.

There was one using an expensive servo motor and 3D printed parts which looks really good.

There was one using a generic sewing machine motor with $20 of snow blower and electrical parts with an O-ring belt but it seemed pretty weak and the belt rubbed itself due to the motor rotation.

Seeing that, I looked for friction drive and saw another but the friction wheel slipped and the side load on the motor shaft was a bit much for my liking.

Some people put a lot of work in to the idea like a guy who posted here and made his motorized with a Hoverboard motor and custom made V-belt pulleys.  That looks really torquey but too much effort.

[SmartShop]

The parts list:

I bought a 100 watt, 7,000 rpm sewing machine motor with foot pedal from Amazon for $15.00.

I bought a 276 tooth 6mm wide MXL belt from Amazon for $5.07.

I bought a roll of foam double stick tape from Amazon for $2.88.

I bought a 15 tooth, 11mm wide, 6mm bore MXL sprocket from Walmart for $6.73.

The total is about $30.  I spent more because I ordered some sprockets from eBay that are 1/4" bore that I won't use and a couple spare belts.

[SmartShop]

How it will work:

I believe the I.D. of the 276 tooth MXL belt will be slightly larger than the hand crank of the Cobbler machine if I twist it inside out (teeth on the outside).

I'm going to line the smooth inside of the belt with foam double stick tape but leave the tape backing on, I'll slide that over my Cobbler hand wheel, align it on the inner edge and then pull out the tape backing to affix the belt to the hand wheel.

The sewing machine motor has a 6mm shaft so I just have to remove the pulley it came with and install the 15 tooth sprocket.

I may have to remove or file down the outer flange on the sprocket but that should be easy.

After that, I just have to make a bracket to hold the motor in mesh with the handwheel belt.

[SmartShop]

The teeth of the belt and sprocket will prevent the motor from slipping.  The 276-15 ratio is 18.4-1, that is a lot lower than the friction drive version I saw (with a 3/4" friction wheel, it was around 9-1).  There will be nearly zero pre-load on the motor shaft, the motor bearings will only have to deal with the forces created by it's 100 watts.

It might be possible to use a GT2 belt with a few more teeth for more gear reduction.  I may try that if I feel like it would be useful.

Another good thing is with an even number of teeth on the belt and odd on the sprocket, wear should be even.

So far I have the sewing machine motor and some extra needles I ordered.  The Cobbler should arrive tomorrow with the belts and tape arriving soon after.  My sprocket is what I'll end up waiting for.

[chrisash]

As the 100 watt motor has most of its power at the top end of it's revs, I question if it will have enough power to slowly go through thick leather 

[Matt S]

I admire your ingenuity and drive. I am curious in seeing the result, though I have an inkling what it may be.

Before you spend too long trying to motorise that machine you might want to get it working the way you want. Depending on the state of whichever one the factory drops on you there might be a significant amount of fettling needed.

What is your definition of "heavy leather", out of interest? These contraptions have some heavy limitations.

[SmartShop]

My hope is that I will have enough power to go through 2-3 layers of nylon strap and the ability to use hand cranking to get through thicker stuff.  That would be "good enough" for me.

I initially thought a big servo motor would be required until I saw the belt drive and friction drive with the 100 watt motor, they did a lot better than I expected and my setup should have a better gear ratio and no slip but the foam tape should create a little give in the system.

I have been looking at the tuning and rebuild videos like those from Turbo Conquering Mega Eagle.  I'm not sure if I will be able to make my base machine as nice as his but I'll try to get as close as I can.

I am pretty mechanically inclined so I think I will be able to make sure the timing is correct, the rest seems to be clean up and deburring with sanding and filing, eliminating slop and reducing friction, all fairly straightforward then I just need to keep it lubed. 

Edited December 8, 2020 by SmartShop

[SmartShop]

When I first saw the Chinese Cobbler, I thought it was cool and would do a lot of the stuff I never did because hand stitching hurts, then I thought hand cranking it would prevent me from doing jobs that need more than several inches of stitching. 

With a motor, the main limitation seems to be the bobbin size and hopefully that is sufficient for the sewing tasks I envision.

Those tasks include belts, small repairs, hemming pants and the occasional pouch/sheath.  I might come up with more ideas if it works well and I get good at sewing.

The last leather project I made was a small but irregularly shaped fitted pouch.  In my mind it was simple but hand stitching it took hours.  It was painful.  The end result was good but close inspection reveals inconsistent stitch length and some puckering.  I mostly got what I imagined but I was disappointed comparing the result with the effort.

Back then, the internet was young, I was poor and as far as I knew a sewing machine capable of stitching leather was $1,000+ so I abandoned leather work and became a metal fabricator for a few years.

If I can tune up and motorized a Cobbler for $150 or less and I know it will handle pretty thick leather (hand cranked), it will be well worth the price.

[SmartShop]

The Cobbler has arrived.

I was expecting the normal bare metal finish on the arms and crank wheel but mine are plated, I'm guessing nickel, maybe chrome.  The rotating foot assembly looks nice too.

The frame casting has a coarse finish and the green paint is not disguising it at all.

Of course the whole thing is covered in Styrofoam fragments from the destroyed packaging.  This is going to take a while to clean up.

First step is to clean it up, then look at everything to see how it works and assess what I need to tune or improve.

I really want to disassemble it completely and refinish the frame, I just need to make sure I have time to do it before my sprocket arrives.  Walmart says it might be here by December 15.

My belts should arrive tomorrow.  Hopefully they will fit with one layer of foam double stick tape.  If not, I will have to order new belts in the right size.  I think I have found 280 tooth GT2 belts and a few other sizes so if the MXL belt isn't a good fit, I may be able to fix that and maximize the gear ratio at the same time but it might change the schedule.

I hope I can clean off the styrofoam, bolt it together and assess the machine by tonight, then I have to figure out how much I can get done by the fifteenth. 

[SmartShop]

About the belts:

MXL has a tooth pitch of 1/12.5" or 2/25" or 0.0800".

GT2 has a tooth pitch of 2mm or 2/25.4" or 0.0787"

The difference might be enough to mess things up with a belt wrapped around a sprocket but with only one tooth engaged on an inverted belt, I am pretty sure that it will work fine, maybe better than an inverted MXL belt because inverting will spread out the teeth a bit. 

[SmartShop]

OK, it's out of the box, almost all of the Styrofoam is removed and my room is destroyed.

After a second look, the chrome on the hand crank side lever has it's plating bubbling and peeling off.  It looks like I'm going to have to sand and paint more than the frame.  Additionally the little sheet metal piece that holds the spring loaded arm for the thread is bent and pretty ugly.

I had hoped for better but for $70, this is pretty much what I expected cosmetically.

I think some of the hardware might be missing, specifically for the stand, probably not a big deal but annoying.

Once I get it on the stand, I'll try to assemble the rest and see if it works.

[SmartShop]

Well, the stand sucks.  I almost tipped it over twice, it is clearly a poor balance job and I may be missing one of the screws that retain the legs but I will be replacing all three because they are too short, the two are "hanging by a thread".

The big problem I have is the shaft the hand crank bolts to got smashed in to the bearing and that deformed the pin key.  After a few taps with a sledge, the shaft slid out of the inner race of the bearing.  The good news is the hand crank is a tight fit on the shaft.  I had to give it a few taps before the nut would engage the thread and snug it up.

Once the hand crank was on, I turned it and met stiff resistance because the needle shaft was clamped too low to the linkage.  After a few turns of a screwdriver to loosen, adjust and tighten, the crank turns but with a scraping noise at certain points.  It seems like rubbing, not binding.

I think this design just needs a few washers to keep the pieces from rubbing against each other.

Compared to the Cobbler of Turbo Conquering Mega Eagle, mine has a shielded bearing, that might not need replacing and my shaft is a tight fit so I probably don't have to make a new one.  The key will probably need replacing and the hand crank keyway is quite oversized I'm not sure how I'll fix that, I may make a key with two diameters and a step.

I'm going to have to watch more videos on the operation to see how to tune it up.  I think I want to start with the rotating needle and foot assembly to clean and lubricate the inside.  Next, I'll probably go after the bobbin assembly and arm.

For kicks, I held up the motor and I think I might be able to make a platform to hold my spool of thread and mount the motor underneath.  The good thing about that spot is it could make mounting and moving the machine simpler.

Eventually im going to have T-slots in the top of my workbench, I plan to make a base that will allow me to clamp it to them for a sturdy support that does not extend beneath the arm.

[kgg]

This is my Chinese Cobbler be readied for strip down to add a longer drive shaft and pulley which will be connected to a motor. The pictures may give you some ideas on adding some attachments.

 

[kgg]

I forgot to add that I added a removable table top (Black thing), main mounting plate, adjustable / removable nose support, 1 lb thread spool holder, a two light swivel lighting holder, scissors holder, better stitch length adjuster knob, a needle position indicator, higher top thread guide, relocated the main tensioner, repurposed the second tensioner as a bobbin tensioner and added a edge guide. This truly is a tinkers machine.

Stay Safe,

kgg

[dikman]

I didn't realise that you had one of these beasties too, Keith. You really like your 3D printer don't you! The small table is a great idea for one of these machines and yours looks very neat.

Smartshop, those legs it comes with are probably great for a street-side repairman in Shanghai, but in general are pretty useless. Most users make up a wooden base to attach it to.

[SmartShop]

For now I need the stand.  Once I have my workbench with the T-slots, I'll be able to make accessories that attach to the workbench instead of the sewing machine itself.  This will make it very modular and flexible and easier to store the parts.  I'm only going to use the machine occasionally so storage matters.

The motor is going to stay with the machine so that mount will be fairly permanent and hopefully as minimal as possible. 

I think I am going to make a mount that uses a toggle clamp style linkage so I can disengage the motor to make it a bobbin winder too.

On YouTube there are cobbler videos by K S Lam.  One is really good and uses a clear cover on the arm to show how the machine loops the top thread around the bobbin to make the stitch.  Another shows a thread holder with an arm that prevents thread twists.  I think I want to do that and also incorporate my motor mount in the same piece.  That's my plan so far.

The motor I have is held together and bolted to the standard mount with two long threaded rods parallel to the output shaft, with nuts on both sides.  Its also about 3.5" long so I'm going to take the motor to the hardware store to see if I can find some kind of 2x4 hanger to use as the pivot point for my motor mount, then a modified toggle clamp to have an over center mechanism to hold it engaged with the hand wheel ring.

My belts should arrive tonight and that Walmart MXL sprocket is coming from LA so it shouldn't be delayed like the sprockets I ordered from China.

I want to bush my arms but I don't (yet) have the lathe and mill I would want to do that job right so I'm looking at ways to do a temporary fix that doesn't prevent me from doing it right later.  I'm not sure if I can do a good temporary fix on the hand crank shaft but I can just keep that well lubed.

[kgg]

16 hours ago, dikman said:

I didn't realise that you had one of these beasties too, Keith. You really like your 3D printer don't you! The small table is a great idea for one of these machines and yours looks very neat.

Thanks dikman, I actually really like the little "Tinker" and the 3d printing helps me solve problems inexpensively on all my machines as well as my other interests.

kgg

[SmartShop]

I did some shopping today and I think I have figured out how to do a cheap tune up that will us an inexpensive material to bush the 8mm shaft without much machine work.

I'm going to leave the 6mm bolt alone for now.  The good news is if that joint wears, it will all get cleaned up when I ream it out for a real bushing.

I got an acorn nut and a toothed lock washer for the 12mm shaft to make it pretty.

One of my belts came in.  It is a looser fit than I had hoped for.  I will probably need two layers of foam double stick tape to take up the slack.

I got a piece of 2x4 and some sort of Simpson 4x4 anchor.  I have decided that my first motor mount attempt will use this.  It will allow me to mount the motor at the back, the sewing machine in the middle and then the base in a more balanced position.  Home Depot didn't have toggle clamps so I might have to order one.

Now the 8mm shaft bushing idea is this: I was looking for plastic tophat bushings but I wasn't finding workable sizes unless they were $2+ at McMaster Carr.  Since I'm going to need at least 2 and I'm not sure how they will last, I decided against that.  What I found that is cheap is polyethylene spiral sleeving.  3/16" with 1/32" wall should do it.  The idea is ill replace the 8mm shaft with a 1/4" bolt that has a nice finish and wrapping it with the spiral sleeve will make it 5/16", very close to 8mm.  With some nylon washers, it should slick things up and the slit in the spiral can even hold some grease.

I think a 1/4" bolt will be strong enough as a temporary fix but eventually ill add better bushings and full size shafts.

[SmartShop]

Well, that was a bit silly, I assumed that the shafts and threads would be common between Chinese Cobbler machines.  Turbo Conquering Mega Eagle had a 12mm hand crank shaft, mine is 10mm.  Also, looking through McMaster Carr, they actually have a good selection of very thin sleeve bearings so I ordered enough to do my 1/4" shaft tune up that won't need machining and enough to do a full size 8mm shaft fix and the 6mm bolt.  I also got a 10mm shoulder bolt to make a new hand crank shaft with and on eBay i found the 16100 size bearings, 10mm pillow block bearings, acorn nuts to cap off all the threads and a couple reamers for installing the full size shaft bushing fix (3/8" adjustable plus 8mm).

By the time those orders were in it was very late and looking at toggle clamps, I couldn't decide which would work for my motor tensioner so I slept on it and after I woke up, the answer was there.  Now I ordered the type I need in two sizes.  Hopefully the little tiny one will be enough.

My belts are still a little issue, they are 6mm wide but my foam tape is 1/2".  I think I'm going to try to slit my tape in half on the roll with a razor blade.  This going to be a double edge razor held in a vise, held in a bigger vise so I can hold the blade 1/4" off a flat, lay the roll on the flat and spin it against the blade to make the slit.

Any way, last night and this morning I figured out a lot of what I'm going to do.  The key for the hand crank shaft is one question that still remains.  I'll measure the keyway in the hand crank and order a pin.

[SmartShop]

Ok, my keyway measured about 5mm so I looked for 5mm, 13/64" and 0.200" pins.  The cheapest shipping from the US option seems to be a pin from a garage door opener chain for $1.00.

I think that does it for ordering parts.  Now they just need to get here so I can do the tuneup job, make one piece for the motor tensioner and then screw it all together.

[SmartShop]

My first attempt at adding a MXL belt to my handwheel with foam double stick tape was a partial success.  It was a bit tricky to get the belt over the double stick tape but after I pulled out the backing, the belt is just a bit loose.  All but about 1/2" sticks but that 1/2" spot makes it a failure.

I'm going to pull off the belt and line it with regular double stick tape (no foam) and hopefully that will take up the slack.

What did work was my tape slitting setup:

 

That is a .2480" gauge pin spacing up a razor blade held in two angle locking CNC vises.

Sorry for the poor focus.

Edited December 11, 2020 by SmartShop

[SmartShop]

McMaster Carr has amazing shipping, my order is already here.

For anyone with an 8mm reamer, you can get a 6mm shoulder bolt with 6mm threads (they typically have smaller threads than the shoulder shank) and a 20mm long shoulder plus a low friction oil impregnated bronze bushing for less than $4.

The 8mm shaft fix is a bit more expensive because I bought stuff to do it twice (first time without drilling and reaming).

The 10mm shoulder bolt looks like it is going to work too but I might have to grind off the head of the bolt.  The 100mm long shoulder might be a hair too short but the stock shaft has no head so it will be fine either way.

With the Japanese ball bearing and a pillow block bearing, I should have precision shafts, bushings and bearings for all of the arms and the crank wheel shaft.

I splurged a little on chrome acorn nuts to dress it up on the crank side.

I'm going to have to strip down the frame, paint it, grind the arms smooth, paint them and make sure everything else looks presentable too.

[SmartShop]

My 8mm shaft is now 1/4" with low friction bronze bushings.  No machining required (on my machine), nothing is overly loose or overly tight and #14 brass washers are installed between every part.  Eventually I will drill and ream out the frame and arms to fit a 3/8" shaft which is closer to the original size but this was quick, easy and cheap.

I'm not trying to change everything to SAE hardware, it's just cheaper here.  My 6mm bolt/shaft is staying 6mm to match the threads in the frame.  My 10mm hand crank shaft is staying 10mm because going inch would require boring out the frame and the cams.  The parts would have been cheaper...

When I fully tear down the frame i'll ream the arms and frame so everything is bushed.

Any way to change the 8mm shaft to 1/4" with bushings, I bought these parts from McMaster Carr:

1x 91259A500

4x 1688K3

And a package of 4 #14 brass washers from the hardware store plus a 10-24 chrome acorn nut from Ebay. 

My 6mm bolt/shaft replacement is waiting on the 8mm reamer I ordered but it uses these parts from McMaster Carr:

1x 90782A115

1x 6679K11

And a 6mm chrome acorn nut from Ebay.  I'll need 3 appropriately sized brass washers.

My 10mm hand crank shaft replacement uses this part from McMaster Carr:

1x 92981A314

And an 8mm chrome acorn nut from Ebay.  I'll need 3 appropriately sized brass washers.  From Ebay I ordered a new Japanese sealed bearing and a pillow block bearing, ill need to make a spacer to hold the pillow block in the right place.  Turbo Conquering Mega Eagle suggested bedding in a bushing to maintain alignment of the hand crank shaft, i think ill bed my pillow block spacer to the frame for the same reason.

My 8mm bolt/shaft replacement is waiting on an adjustable reamer I ordered but it uses these parts from McMaster Carr:

1x 91259A428

4x 2868T56

And a 1/4-20 chrome acorn nut from Ebay.  I'll need 4 appropriately sized brass washers.

[SmartShop]

My partial success is now probably a success.  I added a layer of regular Scotch brand double stick tape on top of the foam double stick and now my MXL belt is adhered around the full diameter of my hand crank.

Once my MXL sprocket and toggle clamps arrive, I'll be able to motorize this thing.