Yet another percision issue

twilliamson
Posts: 13
Joined: Thu Nov 15, 2012 3:48 pm

Yet another percision issue

Post by twilliamson » Mon Dec 03, 2012 2:05 pm

I got my Shapeoko fully assembled and wired over the weekend. Im running a stock Machine with Sparkfun Steppers and a GRBL shield (@13.8vdc). I was running the "Hello World" ShapeOko logo and noticed a problem, the point at which my pen touched the paper and the point at which it should have matched up were off by about 1.5mm(+/-0.5mm). Im also not sure i have my X and Y access set correctly(may have them reversed). My Pen seems to be pretty tightly mounted and stiff. Im not really satified with my belt mounting arrangement so i need to work on that. Could my belts not being 100% tight be causing this problem? The reason i ask it what its going is very repeatable and consistent across the entire logo. I have a picture which I left at home (will upload tonight) of the output. Any Ideas?

cvoinescu
Posts: 4442
Joined: Thu Jul 19, 2012 6:50 pm
Location: Camberley, UK
Contact:

Re: Yet another percision issue

Post by cvoinescu » Mon Dec 03, 2012 2:16 pm

Belts (or V-wheels) could very well be the cause, but it could also be the pen. You often get exactly what you describe with some ball point pens, because the nib can wiggle relative to the body of the pen. A picture of the output, and maybe of your pen and its attachment to the Z rail, would be useful.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

levlandau2
Posts: 187
Joined: Tue Apr 17, 2012 1:52 am
Location: Minneapolis, MN, USA

Re: Yet another percision issue

Post by levlandau2 » Mon Dec 03, 2012 2:32 pm

I would try what cvoinescu said first. I used a sharpie marker for the test. A firm (thick plastic or metal) writing utensil is probably best.

As for the belts, it would be really nice if there was a way to measure the tension on the belt, so a spec on this can be placed. I often wonder if my belts are too loose, too tight or what, but it is hard to be certain without a measurement....

Can anyone with experience using belt tensioner gauges make a recommendation?

twilliamson
Posts: 13
Joined: Thu Nov 15, 2012 3:48 pm

Re: Yet another percision issue

Post by twilliamson » Mon Dec 03, 2012 3:03 pm

I ran my first tests with a sharpie, It Bleed(bled) all over the place, but it too showed the same problem. Thats why I'm thinking it could be the belts, but wanted to pose the question, didn't know if it was a OBVIOUS problem or not ... I'm going to put some thought int a different mounting system for the belt. Im kinda disappointed, every aspect of this machine seems AWESOME, then you look at how they intend you to mount the belt....

cvoinescu
Posts: 4442
Joined: Thu Jul 19, 2012 6:50 pm
Location: Camberley, UK
Contact:

Re: Yet another percision issue

Post by cvoinescu » Mon Dec 03, 2012 3:20 pm

No wonder eight out of ten mods on this forum are about the belts. I'm with you on this one, although the zip tie method isn't that bad. I made some nice (if I can say so myself) belt anchors and tensioners, but I still had problems with clamping the ends of the belt without going way over budget -- so zip ties again.

Anyway, with the stock belt anchors, get the belt as tight as you can. The anchors are feeble enough that they won't let you damage the belt by over-tightening. Someone (I don't remember who) suggested temporarily loosening the bolt holding one of the belt anchors, attaching the belt, then tightening that bolt back. You can even bend the anchors outward to tension the belt while the bolt is loose, to avoid detaching and re-attaching it.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Improbable Construct
Posts: 997
Joined: Tue Apr 10, 2012 3:21 am
Location: Fairhope, AL
Contact:

Re: Yet another percision issue

Post by Improbable Construct » Mon Dec 03, 2012 3:50 pm

I don't know what the belts are made of but they are very strong. I have mine pulled so tight you can pluck them like a guitar string. I have been running them like this for months with only one little problem. The tension on the belts was causing the nylon spacers on the idlers to warp and bend. I replaced them with aluminum spacers. No more problems.
Shapeoko #Classified some of the bolts may be original parts.
Shapeoko 1 # ???? Stainless plates, still in the box.
Shapeoko 2 # 3926 not stock
Shapeoko 3 # 0003
Store:
http://ImprobableConstruct.com
Twitter:
https://twitter.com/ImprblConstruct

cvoinescu
Posts: 4442
Joined: Thu Jul 19, 2012 6:50 pm
Location: Camberley, UK
Contact:

Re: Yet another percision issue

Post by cvoinescu » Mon Dec 03, 2012 5:30 pm

I actually use the sound they make when plucked to tension both Y belts equally. They're not terribly tight, but tighter than they get with the stock anchors for sure. They're perfectly fine; I'm more worried about wearing out the motor's bearings prematurely than of anything happening to the belts.

The belts are made of rubber sandwiched between nylon fabric (to reinforce outside surfaces, i.e. the teeth), and reinforced with very tough glass fiber running lengthwise. The glass fiber is what gives it the resistance to tension. Interesting factoid: toothed rubber belts are manufactured as a long tube the diameter of the belt (if a closed belt). The rubber is extruded. Many diameters are made, and the closed belts are made by cutting a tube of the right diameter into slices of the desired width. Open-ended belts are made by slicing one such tube in a spiral (helix), so very long lengths of belt can be made in one piece from a reasonably-sized tube. The tube is large enough that the slight slant of the teeth is unnoticeable.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

levlandau2
Posts: 187
Joined: Tue Apr 17, 2012 1:52 am
Location: Minneapolis, MN, USA

Re: Yet another percision issue

Post by levlandau2 » Mon Dec 03, 2012 10:36 pm

@twilliamson:

Do you have dual y-axis (a motor on each rail of the y-axis)? Maybe you are getting some slop from not having the left and right y-axis synchronized...?

PsyKo
Posts: 430
Joined: Thu Aug 30, 2012 8:42 pm
Location: France

Re: Yet another percision issue

Post by PsyKo » Tue Dec 04, 2012 9:50 am

Hi,

When I ran my first job, I was doing the same. Using a pen, more or less well secured on the Z axis makerslide. It turned out to be pretty messy, mainly because of the pen or the pen being lose on the makerslide.
After a few disappointment, I tried with the rotary tool, tightly secured and the accuracy increased a lot. It's quite a gap to switch from a pen to a tool, but it's worth it.
Maybe you'll get more accurate result with a decent pen holder.
Shapeoko #736
Kress 800, Z Axis upgrade, dual Y, 600mm X&Y rails, metal spacers and V Wheels, home switches, 4th axis
Goko - Free CNC Control Software - http://www.shapeoko.com/forum/viewtopic ... 380#p44380

twilliamson
Posts: 13
Joined: Thu Nov 15, 2012 3:48 pm

Re: Yet another percision issue

Post by twilliamson » Tue Dec 04, 2012 1:13 pm

This is the Issue i seem to be having.
Image

I ran the job twice with the same setting a 0(home) position, I wast looking to see how repeatable the machine was
Image

Now these jobs where run with the S at the front of the machine and the O at the rear so ShapeOko was down a side with the makerslide, I think i have my x/y reversed.
Last edited by twilliamson on Tue Dec 04, 2012 1:40 pm, edited 1 time in total.

Post Reply