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Constant velocity
« on: August 06, 2014, 05:38:30 AM »
Hi guys
New to the forum so I apologise if this has already been covered....

I've been using mach 3 on my diy router for some time but I've just started a cnc quilter for the wife.

How do we set mach 3 so it always runs the same speed? As it's going to drive a sewing machine with a constant stitch length we need to make sure the speed, velocity is constant. I clicked the CV box on the setup page but it didn't really make much difference.

Thanks for your help.
(I'd appreciate any links, tips if some knows about diy cnc quilting)


Offline Hood

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Re: Constant velocity
« Reply #1 on: August 06, 2014, 04:57:04 PM »
Dont know anything about quilting but if your code has direction changes and lots of short lines of code then your acceleration may well play a big part in how things run. Basically the faster the acceleration the better, assuming your machine is rigid enough to cope.

Re: Constant velocity
« Reply #2 on: August 07, 2014, 10:51:13 AM »
Hi NJ Lowie
Hi Hood

It may help to think of a quilter as a tube of toothpaste squeezing out material. You have to match the flow of the material to the feed over the surface you are applying it to.

A conventional sewing machine has a feed mechanism that is mechanically linked to the stitching mechanism. slow the stitching down and the feed will slow down in perfect unison.

Quilters are big. Very big. A large industrial one will have a moving mass of hundreds of kilograms. I had one that had a moving mass of about 500 kg. When it slowed down to turn a corner or reverse direction the stitching head had to slow down too. The stitching speed and the feed were not mechanically linked; the X-Y feed was CNC driven by a proprietary control system that maintained the relationship.

Quilters usually have not very stiff RHS Steel frames and a heavy sewing head, they flex. Fast reversal is not an option or they will shake due to vibration in the system. They have to be slowed down and then accelerated slowly.

A typical Sewing machine working as a quilter has a top speed of about 4000 RPM the length of one stitch is about 2.5mm (1 Stitch per Rev) That gives a top feed rate of 2.5 x 4000 = about 10 metres per min or 32 feet per min imperial down to about one stitch per second 60 rpm for "tacking" (At the start and end of a run to tie off the ends of the cotton to stop it unravelling).

The ratio must be kept constant to avoid the space between stitching holes changing.

A stitch length of 2.5mm is nominal depending on the work it can be as low as 1.5 and as great as 10mm for heavy mattress work or stitching polishing mops and other industrial products quilters are not just used for bedding. Many Car seats faces are CNC quilted. As are train and Plane seats, also Clothing, Parkas and dressing gowns etc.

I have never seen a satisfactory solution for this application using Mach3. Considering the (Thousands) of industrial quilters in the world and an order of magnitude more quilters that work from home. It would be a good problem to solve.

« Last Edit: August 07, 2014, 11:09:39 AM by John Mac »
Re: Constant velocity
« Reply #3 on: August 07, 2014, 11:16:05 AM »
PS:  This discussion on the Mach forum is worth reviewing.

Re: Constant velocity
« Reply #4 on: August 07, 2014, 09:13:34 PM »
Thanks guys

Starting to get on top of it now, after many pages of this forum. A great source of info, thanks again to all.

Anyway it's only a small lite frame setup, guilts about 2mtrs by about 150mm which is limited by the machine size (see other post) so acceleration shouldn't be a big drama.
I've maxed out the acceleration and set cv to .000001 and it now travels at reasonably constant speed, I'll just have to find the maximum velocity it can comfortably run at. 

Even though I've been using mach 3 for a few years now it's not until you try a new project that you realise there is soooo much more to this software!

I'd love some feed back on my other post about using one of the axis to turn the roll holding the quilt.....

Cheers for now, Dave