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.