I added a motor to one of those cheap leather patchers

[polyfractal]

Hey everyone...longtime lurker, first time poster

I recently picked up one of those cheap chinese leather patchers, and as a fun shop project decided to add some v-belt pulleys and a motor so I wouldn't have to hand crank it anymore.  I thought folks here might like to see the final outcome, testing it with a few layers of leather and looking at the stitch quality.

Animated gif of the machine operating: https://i.imgur.com/8D0ZGKZ.gifv

Sewing test with leather: https://www.youtube.com/watch?v=eWmX6pZ1bA4

For whatever reason, I was under the assumption that DP-35 / 134x35 needles would work in the patcher... thought I had read that somewhere.  Well, they are too long and it messes up the timing.  Luckily you can just cut/grind them to size and everything works as expected, even though they don't have a flat.  I found a lot more chisel point options in DP-35 than Hax1, as well as larger sizes.  In the video I'm using size 69 polyester thread, but have used 92 as well.  The leather being tested is maybe ~4oz oil-tanned pullup.  It's not supple, but not super stiff either. The four-layer test was about 7.5mm thick.  I should have grabbed some stiff tooling leather but didn't think about it in time.

All in all, the project was fun and a good practice project. Learned a lot along the way, and everything even mostly works Some issues like awful runout on the motor pulley, but all unimportant given the application, so I'm happy with how it turned out.

If anyone is interested in the build itself, I essentially fabricated a v-belt pulley that mounts on the cast iron crank flywheel.  A smaller cast pulley is mounted onto a "hoverboard" hub motor. These are cheap ($30 new, $15 used) brushless motors that have crazy high torque relative to their price (7-12Nm). They are designed to direct-drive humans around at low RPM, so they are perfect for something like driving a slow speed leather machine. It's a brushless motor, so can be controleld with a cheap hobby ESC and servo tester (for PWM signal). Right now everything is just bolted down to a 2x4 and clamped to my bench, but I plan on making a nicer tripod since the one that came with the machine is garbage.

Edited February 21, 2019 by polyfractal
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[Yankee63]

Hi there, you call it a patcher. Can I ask why? Brand name?

I have looked at those machines on ebay. Do they stitch well?

I like the motor conversion.

I hand sew all my projects and have been looking for a machine to speed up my sewing.

What is your opinion of that machine? Will it last?

Thanks for the help.

Doug

[polyfractal]

I think they are called "patchers" because they are often used to sew patches onto jackets (due to long arm being able to reach down sleeves, heavy duty to go through thick leather jacket, etc).  Or potentially because they are used to "patch"/repair bags and boots  They are also called "cobbler machines" for the same reason.

They are knockoffs of old Singer 29k's, and are just generically manufactured in china (hence most people call them "chinese patchers").  I think there are some folks that import the machines and perform quality-control/tuning and resell them.  Mine came undamaged and complete, but you hear about other people receiving machines that are missing crucial components or are totally beat up in shipping.  So the importers doing QA make sure that doesn't happen.  I believe "Able 290" is one of those resellers... think the fellow who does it visits this forum too iirc.

Stitch quality is remarkably good imo, considering how cheap they are.  Nice and even, tension is good once you get it dialed in.  There are a few caveats though:

• Backstitching is tricky because there's no reverse... you have to swing the foot around and get it lined up exactly
• There's no dial for stitch length, just a bolt and nut that you adjust.  So repeating the same stitch length is not easy.  I'm thinking about making a dial to replace the nut for more control
• Same issue with foot pressure and tension
• Bobbin is rather small, so thicker thread will exhaust the bobbin fairly quickly
• Teeth on the foot are very aggressive and can mar leather.  Most people file those down, or dip them in plastidip or similar

I think the machine will last a long time, it's super simple and heavy casting.  But it is a crude machine.  Lots of sharp edges that need filing, everything is covered in thick, waxy cosmoline, casting is very rough and parts need to be cleaned out and re-greased/re-oiled.  The biggest downside in my eyes are the hand-cranking nature: cranking by hand is not very smooth, and you have to "build up momentum" to get through thick leather.  Which means it's hard to accurately guide your work with just one hand.  Hence the motor conversion

I'd say it's more of a project machine if you enjoy fiddling/tuning/tweaking, and less of a "production" machine where you just want to sew leather and forget about the machine itself.

Edited February 21, 2019 by polyfractal

[dikman]

Polyfractal. an interesting project. As for needles, mine uses standard domestic needles, cheap and easy to find.

[Yankee63]

Sounds like I'm gonna look at amazon to see if they sell it.

At least Amazon will stand behind what they sell.

Thanks, it will be a fun toy to tinker with.

Doug

[bikermutt07]

Interesting post, and welcome aboard.

What size shafts do the hover boards run?

Sounds like a good motor for a low speed burnisher.

[chrisash]

With the tyre still on, you could just use friction for a direct connection and do away with the belt

[polyfractal]

12 hours ago, bikermutt07 said:

Interesting post, and welcome aboard.

What size shafts do the hover boards run?

Sounds like a good motor for a low speed burnisher.

It's a 16mm diameter shaft, D-profile.  And about 50mm long.  I have a few other of these motors (randomly purchased from ebay, so probably different manufacturers) and they all appear to have the same shaft dimensions.  They work out to be about 16 kV motors, so at 48v they are in the ballpark of 700-800 rpm. 

The tricky thing is that these are "outrunner" motors, meaning the rotor spins rather than the shaft.  So the shaft is bolted stationary (and all the wires feed out of it), while the rotor and bell rotate.  That's why I had to mount the pulley to the exterior of the motor.

 

4 hours ago, chrisash said:

With the tyre still on, you could just use friction for a direct connection and do away with the belt

Hehe yeah, I considered that.  Was afraid it might slip under more difficult conditions (thick tooling leather and similar).  A v-belt has about half the larger pulley's diameter and a third of the small pulley for friction surface, whereas a direct friction drive would just be a single contact point.  The other thing that gave me pause is the cast iron crank flywheel itself.  There's a lot of play between the machine's shaft and the flywheel, so I was afraid the wobble/runout would cause the friction drive to slip as well.

Also... this was predominantly an excuse to practice machining (I'm new to the hobby), so part of the fun was fabricating the components

I actually considered rebuilding the machine to be direct-drive: mount the motor directly to the crank flywheel.  The motor has plenty of torque to direct-drive, but it introduced a lot of other difficulties.  The nature of the hubwheel would have made mounting a shaft adapter trickier/more precision required. And I would have had to investigate cooling the motor. Brushless motors will happily pump as much current through their windings as required to meet the torque demands... and at slow speeds that means there is little airflow cooling the coils.  You can easily overheat high torque, low rpm motors without active cooling.

[chrisash]

They definitely look great motors and i guess could be used for all sorts of projects

Thanks for the info

[vpd66]

Good job! Keep updating us on this style sewing machine. I think these are great machines for hobby use and I love reading about people upgrading and having success with these Chinese patchers.

[dikman]

They sound like interesting motors to play with, but the biggest issue I see is getting a suitable power supply to run them.

[polyfractal]

15 hours ago, dikman said:

They sound like interesting motors to play with, but the biggest issue I see is getting a suitable power supply to run them.

Yeah for sure, DC power makes life interesting. Lots of folks repurpose these Cisco networking power supplies because they are cheap and available anywhere from 400W up to 4kW ranges (and most accept both 120/240v): https://www.ebay.com/itm/CISCO-CATALYST-6000-1300W-AC-POWER-SUPPLY-SPARE-P-N-WS-CAC-1300W/222162589697

Other server and computer PSUs are pretty commonly used for the same reason; mass produced and cheap, DC voltage in the right range (12-60v), usually run off 120v.  Not as convenient as a bench supply but not too hard to use after some fiddling.

[dikman]

That ad lists shipping as $451 worldwide!

[Wizcrafts]

57 minutes ago, dikman said:

That ad lists shipping as $451 worldwide!

Shipping:

$15.45 Standard Shipping

[SilverForgeStudio]

Very nice conversion- I have one as well- Similar results in stitching practice but have not converted mine to power yet- thanks for the video

With the DC power supplies you can always visit an camper/RV store as they power supplies are all 24 or 12 volt for plugging into the towing vehicle.