Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: cut2spec on April 09, 2009, 07:43:38 PM
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I have bought a 2X4 router and have completely rebuilt the machine it was very cheaply made. I was cutting ovals and it looked like I chewed them out (polycarbonate). Now I can cut a perfect (by eye) circle and it has a very smooth finish. One more problem to overcome, I hope.
I am cutting polycarbonate. I am cutting two pieces that are to be assembled to gather. This is where the problem lies. The two pieces do not line up; the gears that go inside don't fit. I took the g-code and cut the pieces out on my CNC milling machine and they are perfect. So I am assuming this eliminates the g-code. Info on the router; Mach 3 – steppers - rack and pinion - Bosch palm router. Can anyone point me in the right direction of where to look.
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Can you post a pic of the parts, might gives us a clue as to whats wrong.
Hood
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I am on my way to the shop I will post them when I get there thanks
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You will have to try again with posting the pictures of the parts. Nothing saved.
Tweakie.
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one more try
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heres them side by side you can also see a finished product on cut2spec.com
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I just checked my steps per uint with a dial indicater it seems to be moving the same amount each time
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mach 3 verison R 3.00 is what I am using on the router I compared the part from the milling machine and the part from the router there is almost .250 difference in length
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Not really sure what I should be seeing in the pics as I dont know how they differ from what they are meant to be.
Just wondering if you have any offsets for the tools in the router, that could possibly account for it.
Hood
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How do I check the offsets? I will try to explain the pics. The two parts are riveted together, when I do this the out side edge of each part do not match. I get something different everytime I cut it. It is the same drawing for each side. The parts lined up perfect on my other machine. It is like the steppers are losing a step or mach 3 is giving the wrong signal. I think I have eliminated this possibility buy checking the steps per unit with a dial indicator. So I am at a loss. Could the mach 3 be set up wrong The computer and mach 3 came with the router.
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It wont be offsets if each time is different, more likely it is losing steps due to motors being tuned too high, try lowering the accel a bit in motor tuning, remembering to save each axis as you go.
Hood
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I will try this and let you now thanks
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the accel is set at 180 do you have a suggestion what to change it to also should I change the velocity from 250
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Its hard to tell, especially as I have always had bigger/heavier machines and they are set in metric. For my stepper Bridgeport I cant actually recall the exact accel but I think its something like 50mm/s/s so for your imperial that would work out around 127in/s/s.
These numbers are however meaningless as they are on two totally different machines, different drives, motor weights types of axis etc etc etc.
What I would do is drop the accel by half and see if it makes a difference, if it does then start increasing again until you find the sweet spot.
Hood
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I adjusted the accel to the sweet spot of 125. This improved the running of the router a lot. And seemed to improve the cut a little. but we are still having a problem I am going to post some more pics to try to explain the problem where it stands now. I cut it out of black poly on my milling machine and the lastest cut for the router I did in wood to show you the contrast. You can see in the pics that sum edges line up good and the others are smaller.
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Have you checked to make sure your steps per unit are set correct?
Hood
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That is where we are. But we are having trouble figuring this out. Are 1" gear has a 16 pitch but we don't know how many pulse per rev are steppers are. How do we determine our pulses per rev
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Steppers will usually be 200 steps per rev but less commonly also come in 400 steps per rev. You will also then need to take into account the drives as they will most likely have some sort of divisor. They could be full stepping, half, 4, 8 10 or more microstepping.
One other thing to look at is see if you have backlash enabled, if you do make sure it is set up right or better disable it as a test.
Hood
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Backlash was not enabled. Our steppers are 200 and our drivers are set at 1/8 so we calculate 1600 pulses per revolution. Since we are using a 1" gear, 16 teeth we calculate that we are traveling 3.1415 inches per revolution. We then calculate that our steps per inch should be at 509.3108. Are we on the right track? We'll run a new part and see what we get with this setting.
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That sounds about right.
Hood