Archive for September, 2020

CNC Fabric Cutterhead Prototyping: More Torque (Less Speed)

Monday, September 21st, 2020

The previous cutterhead prototype from about a year ago that used a tattoo gun motor reciprocated the blade at a high speed and cut the fabric well, but stalled easily in the foam spoilboard. I needed more torque and I was hoping I could get by with less speed.

micro gearmotor

And now I remember how I stumbled across the idea to use a tattoo gun motor — Nick Poole’s SparkFun post on building a tattoo gun from one of their cute widdle gearmotors, which are available in a wide range of gear ratios and output speeds. So when the tattoo motor didn’t have enough torque, I ordered two different speeds of the micro gearmotors from SparkFun, following Nick’s path of innovation.


Prototyping a CNC Fabric Cutterhead

Sunday, September 20th, 2020

If I’m going to try to develop a CNC fabric cutter, it’s going to be called the CutterRouter.

There, got that out of the way.

If I’m going to try to develop a CNC fabric cutter, at least the prototype and ideally the final version will use all commodity components plus easily-fabbed parts (3D printing, lasercutting, easy woodworking with common shop tools and not requiring a high degree of accuracy). The self-imposed choice of commodity components makes me want to use a readily-available X-ACTO® blade as the knife.

If I’m going to try to develop a CNC fabric cutter, I want to develop a working prototype cutterhead first. It’s the only part of a CNC fabric cutter that’s significantly different than a 3D printer or mill. So if a cutterhead can be made to work, the rest is easy; if it can’t be made to work, the rest is moot.

prototype reciprocating-blade cutterhead


CNC Fabric Cutting

Saturday, September 19th, 2020

Surely by now the sewn-product industry has CNC fabric cutting?

Yes, but I don’t know much about it and my acquaintances haven’t worked at places that use it. What I’ve been able to find appears to start around $30-40K for a fairly short table, with extensions available. That entry pricing only makes sense for a fairly high volume of product.

Could we do better, and is there a market for it if we could?


How Fabric Is Cut for Product Development and Made-to-Measure Production

Friday, September 18th, 2020

In the sewn-product industry, product development can have a rapid-iteration phase that would be familiar to anyone in hardware or software development. Whether it’s testing the fit and strength of a new backpack or checking the fit and appearance of a garment on the fit model, a single prototype at a time may be made and revised weekly, daily, or even more often.

In the garment industry, “made to measure” refers to clothing whose pattern is made from measurements of the individual wearer and then either drafted algorithmically or pieced together from library parts for each possible value of each collected measurement.

In product development and in made-to-measure production, a number of factors of fabric cutting are different than in mass production:

  • The manufacturer or producer may be making a single quantity, certainly only a small quantity.
  • The manufacturer or producer is unlikely to be making multiple sizes at the same time.
  • The above factors rule out the long markers used in mass production.
  • The above factors rule out lay-ups of many plies of fabric.
  • The manufacturer or producer may not even have a marker — pattern pieces might be hand-drafted and on separate pieces of paper or oaktag (card stock).

I can’t speak definitely about every possible cutting scenario in product development and made-to-measure production, but I can cover common cases.


How Fabric Is Cut in Industry

Thursday, September 17th, 2020

Eastman Class 134 rotary fabric cutter

I volunteer in the sorting room at my local thrift store about once a week and a few years ago, one of the guys who processes electronics and appliances showed me this thing out on the sales floor and asked whether I knew what it was. Pizza cutter? Linoleum cutter? Don’t know; but it’s a beautiful piece of machinery, so I bought it.

By the time I left the store that night, we’d figured out together that it was a fabric cutter. And as it happens, by now I know a lot more about the topic than I did then.


Vintage ED-Lab Prototyping Station

Wednesday, September 16th, 2020

Spotted at a thrift store.

Of course anything with that many knobs and jacks caught my eye, and it’s in fantastic cosmetic condition.

Looking more closely, the function generator would have been a dream to have when first learning about op amps!

MakerBot CupCake’s Triumphant Return, Part Before 1: The Z-Axis Stepper Motor Is Getting Old

Tuesday, September 15th, 2020

Back in 2018 when I got the CupCake out to fix the extruder-stall problem from 2014, it had a new problem of the Z motor not doing what it was asked. The stalling motor was enough to stall me for another couple of years; or was the skipping motor enough to cause me to skip ahead to 2020 for further diagnosis?

top of MakerBot CupCake

The CupCake’s extruder mounts on a Z stage that lowers down to the build platform. The Z axis is run by a stepper mounted inside the frame at the front, with the central black pulley on the motor shaft driving the belt that connects the four black pulleys on threaded rods protruding down into the machine to raise and lower the Z stage by its corners.

As I was testing in 2018, and again this spring, what should have been continuous movement of the Z axis getting down to the platform to start a print would once in a great while pause and resume. I didn’t hear the characteristic clack/clonk of a stepper motor skipping steps, but it was hard to be sure. But whatever the cause, if the Z motor wasn’t running completely reliably before a print, there’s a fair chance that it could misbehave during a print. Plus a printer with neither Z probe nor Z endstop makes it hard enough to set first layer height already; I don’t need to play this game in Nightmare mode.

Part of the challenge was replicating the problem. In the first run at Cort’s house, everything worked initially, then finally misbehaved many minutes into a print. After restarting the print, again it took many minutes before the next failure, suggesting that we were going to have a dickens of a time watching the problem on a scope and reinforcing my decision to take it to his house where we could use his digital scope with triggered capture.

However, after some fiddling, we discovered that if I used the ReplicatorG control panel to continually jog the Z up and down, at least after the printer was warmed up, it would occasionally pause, which we could hear as well as see. That in turn led to an even more interesting discovery.


Engineering Construction Set, Part 1: Sticks and Brackets

Monday, September 14th, 2020

2020 extruded aluminum (so named for its 20-mm-square cross-section and not, confusingly, for the year that I bought it) and its larger siblings seem to be the preferred current construction set for engineers. Each face of the aluminum sticks has a T-slot that accepts a nut or the head of a custom machine screw, allowing the sticks to be fastened together without drilling holes and thereby facilitating rapid physical prototyping.

2020 aluminum extrusions and 8-mm lead screws

I recently ordered a stack of 2020 extrusions pre-cut to several lengths I wanted to play with. It was my first foray into AliExpress, which (that particular foray) went quite well. The tidy pile above cost me only a little over $100, the best deal I could find in several places I looked.

2020 aluminum extrusions with 3D-printed corner bracket

Since receiving that shipment, I’ve been prototyping brackets for attaching 2020 extrusions together. Shown here is the overly elaborate last one I’ve tried, because I didn’t get good pictures of the earlier attempts in action.


MakerBot CupCake’s Triumphant Return, Part 1: The Extruder Motor Is Getting Old

Sunday, September 13th, 2020

After lo these six long years, I now have the fixes and the knowledge to get the CupCake to complete a print.

3D prints at different nozzle temperatures

Back in January of 2015, I had got my CupCake tuned up for pretty prints and then the extruder stopped working. Two years ago when I documented that experience, I got the CupCake set back up to troubleshoot that extruder problem and I had a new problem with the Z motor skipping steps, which I had to solve before I could figure out why the extruder stopped working 40+ minutes into a print.

I figured that troubleshooting the two problems would be easier with a fancier scope than I have; so a few times this spring, carefully observing COVID-19 precautions, I made couple-hour visits to my friend Cort and his basement workshop. Over the course of those visits, we were able to identify and address the Z-axis problem (which I’ll write up later) and make some observations about the extruder that ultimately led to a successful workaround this weekend.