holy tape for liner drive

[wayword son]

my project is a two axis large format plotter (66" x 40") used to draw kite sail templates,as well as to hot cut the nylon. essentially the idea is to move a pen or a soldering iron around on the table, to draw or cut the pattern. a tolerance allowance within about +/-1/32" would be good, +/-1/64" would be perfect, any tighter than that would be showing off.

a gentleman on my kite builder forum posted this idea, which gave me the tough that CNC was economically possible under the rule of the KISS method of engineering
http://www.vvveaz.nl/projecten/vlieg...r/plotter.html

the gentleman used old printer parts, and drives the x axis with diy perf. tape made of Dacron mainsail cloth, he claims an accuracy of about +/- 1mm, which is good enough for kites, but i hope to improve it a little, so I'm not waisting machine time readjusting the tool head all the time.

i just read the tread the gentleman posted on the slicky salesman, and his metal tape system, and though a good alternative for me would be two layers of Dacron ribbon, reinforced with a few runs of "spectra" (in Europe, "dyneema") braid. i can easily "tape" and sew the braid in, then hot cut holes 1" apart with a soldering iron. the benefit of using the fiber over s/s is it can be "machined" with simple jigs and tooling, that is relying on what i have (sewing equipment, and kite making supply's) rather than what i don't have (machining equipment) is unaffected by heat, and has minimal stretch when put under the right tension.

this was going to be my source for the drive wheels, turned to a 4" circumference, with four .125 holes for metal pegs. http://www.kitebuilder.com/catalog/p...5d9e4d063933f7

my questions would be how much do i reduce the drive from my motors for a reasonably adjustable speed range, @ 4" per turn. (using linsteppers as drivers on a 1.8deg motor)

does anyone have experience using the slide bearings, and aluminum T rails offered by 80/20 inc. and are the systems suitable for light duty CNC.

[RICHARD ZASTROW]

wayword son, You might want to look up "drive tapes" at Belt Technologies Inc. They have perforated or non-perf. metal tapes that have very limited stretch etc. They are used for very similar applications to yours.

[OCNC]

Originally Posted by wayword son products_id/1036?osCsid=8c3cadc5f70d3ed5c75d9e4d063933f7[/url] my questions would be how much do i reduce the drive from my motors for a reasonably adjustable speed range, @ 4" per turn. (using linsteppers as drivers on a 1.8deg motor)

It's been my experience that steppers start to noticeably lose torque at rotational speeds above 3 revs per sec. Direct drive at this rate with 4" circ. wheels would give you 60 feet per minute (10 feet in 6 sec.). I doubt that you would want to go slower than this for plotting but I have no idea what feed rate is required for hot knife cutting. Since in general this machine is pushing such a light inertial load against a non existent resistance when plotting and a minimal resistance when 'cutting' you might want to gear up to 120 fpm (20 feet in 6 sec.) or even 180 fpm (30 feet in 6 sec.) assuming you won't expect to operate above a 3 rev/sec stepper rate. You can then slow down in software with a torque gain (steppers rotating less than 3 revs/sec).
The gist of this is to biuild your top end speed into the hardware and don't rely on going faster in software (although you in fact may be able to).

Interesting links by the way. Thanks for posting those. There are some fiberglass measuring tapes usually starting at 50' length that might work for a tape drive system but I've never tried to place a hole in one of them.

Chris

[greybeard]

Just for info, I'm building my x axis around a couple of dead digital tape measures (Bosch DMB5) I got of ebay for £2.
5 metres of steel tape with a 2.5mm hole at 1cm intervals.
The drive wheel will be 8 ball bearings epoxied into grooves around the circumference of a 1" diameter collar on the stepper shaft, using a short length of the tape as a wrap-around jig.
I did think of using a 16 tooth gear wheel as the base for the balls, but couldnt find one in my junk box.
John

[wayword son]

Originally Posted by OCNC It's been my experience that steppers start to noticeably lose torque at rotational speeds above 3 revs per sec. Direct drive at this rate with 4" circ. wheels would give you 60 feet per minute (10 feet in 6 sec.). I doubt that you would want to go slower than this for plotting but I have no idea what feed rate is required for hot knife cutting. Since in general this machine is pushing such a light inertial load against a non existent resistance when plotting and a minimal resistance when 'cutting' you might want to gear up to 120 fpm (20 feet in 6 sec.) or even 180 fpm (30 feet in 6 sec.) assuming you won't expect to operate above a 3 rev/sec stepper rate. You can then slow down in software with a torque gain (steppers rotating less than 3 revs/sec). The gist of this is to biuild your top end speed into the hardware and don't rely on going faster in software (although you in fact may be able to).

if i figured this right, the first speed is 20" per second, that is about 2 x as fast as hand cutting a single layer of nylon, and the cutting speed goes down from there for heaver or multiple layers, which helps, because i get a torque increase when i lower the speed. so, can likely do a 1/1 drive ratio, or maybe a 3/2 or 5/3. the linstepper is rated to do 1200 or 1800 step motion, which stays well within my tolerance levels on a 4" linear cog

Interesting links by the way. Thanks for posting those. There are some fiberglass measuring tapes usually starting at 50' length that might work for a tape drive system but I've never tried to place a hole in one of them. Chris

not sure theres a way to perforate fiberglass cloth and maintain strength. the beauty of a double layer of 3.9oz Dacron, is it is fairly non stretch, and when you burn a hole through it, it welds it together, and around the hole you get a layer of solid polyester plastic, which allows it to maintain hole strength, when i have to run a line trough a kitesail to get it to an atachment, usualy i have a dacron pach where i melt a hole, forming a quick, and cheep "gromet" done this way the holes should keep without tear out or fraying, i can also if i wish, sail tape, and sew Kevlar ribben on either side of the hole layout, which would give it a stretch Resistance superior to steel by weight, (makes me wonder whether perf. kevlar belting has been tried?)

Originally Posted by greybeard Just for info, I'm building my x axis around a couple of dead digital tape measures (Bosch DMB5) I got of ebay for £2. 5 metres of steel tape with a 2.5mm hole at 1cm intervals. The drive wheel will be 8 ball bearings epoxied into grooves around the circumference of a 1" diameter collar on the stepper shaft, using a short length of the tape as a wrap-around jig. I did think of using a 16 tooth gear wheel as the base for the balls, but couldnt find one in my junk box. John

the idea of using measuring tapes must be great for layout (its already marked for drilling!) i think i will try your idea of using ball bearings, if i get an abs Tinkertoy fitting, the right epoxies will stick to it, and i can have the holes in my drive cog drilled shallow, but I'm still going to use the Dacron, rather than metal, I'm confident enough in my manhood to admit to knowing how to sew, and once i have the jig put together, melting holes should be a quick process (like a hot knife though butter so to speak) and i have a lot of dacron (a 18x54" sheet)

[wayword son]

hi all, just an update

i got my motors in, these are the specs.

6 lead full/micro step hybrid stepper motor
step deg. 1.8 (200/rev)
static torque 60 oz-in
rate amp 1.0
rate volt 5.00
ohms / phase 5.00
induct./ phase 8.00
rotor inertia .63 0z-in

i'm going to use a linstepper controler,
im prety sure these will drive a simple ploter/hot cutter with torque to spare, if this is just a pipe dream, please chime in.

on the stepdown, after working with some cutting for ongoing pojects i have decided that a 1/2 ration on a 4" circumfrence cog weel will work nicely, any faster feed rate and i may have to crank the heat to high on the iron to cut the nylon cleanly.

for the slide, i'm thinking skate bearings, and steal angles (triangle up) on one side, and just rollers flat with no track on the other, but bothe sides driven (like the cutter i refrenced in my first post) i may make the gantry out of square tubing steel, or aluminum (if the steal is to heavy). the tool head will likly be on more skate bearings

thank you
Jon

[rippersoft]

If you put 2 skate bearings together on a single bolt with a spacer in between the bearings, you get a poor mans' v-bearing. Rolls very well on angle iron or the lip of unistrut (u channel) steel.

The bearings sit far enough down the side of the angle that it is pretty hard to cause them to not hang on. I use about a 1/4" spacer.

As for reliability, if you run your machine constantly with alot of load, then maybe the bearings will fail. However, how often do people replace the bearings in their rollerblades?

Use ABEC-5 or ABEC-7 if you are concerned about bearing strength and wearability.

RipperSoftware

[wayword son]

thanks for the idea rip

as its a plotter, not much issue with wieght, and zero backlash from the tools. so a light wieght bearing is ok.