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Chain Drive - Velocity & Accel Setting

Chain Drive - Velocity & Accel Setting

Postby kevinl » Mon Jan 25, 2016 3:58 pm

I moved from a threaded rod machine to the chain drive. I've seen post about running Velocity - 400 & Accel - 5..

I've tried 400 & 5 but the gantry seemed like it was slow in stopping and changing direction.. I like the sound and the way the machine acts using 300 & 10.

it's using the 400 in oz motor on the x axis for now and it's a 4' x 8' table v-groove bearing on alum angle, Mach3..

what's others experiences and comments..

sidebar comment, don't know if I really want 400 ipm in a G0 move.. 300ipm in a g0 move already routed off part of the insulation on the router cord when I was playing/testing..
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Re: Chain Drive - Velocity & Accel Setting

Postby Awesomeness » Tue Jan 26, 2016 2:31 am

10 acceleration on my machine caused lost steps. Once the machine would heat up (motors become less efficient/strong when hot), it would shudder and crash. Yes, the machine will seem to accelerate slowly, and coast to a stop, compared to screw drive. Screw drive has a tremendously bigger mechanical advantage, which makes it accelerate quicker, but have a lower top speed.

As for the top speed, you can probably even go faster than that. I have mine set to 600, with 425 in*oz motors. It really only ever moves around that fast while rapiding between cuts, since the toolpath will give it instructions to only move at a feedrate of <100 ipm in most materials.

Ultimately, the decision is yours. Push your machine as hard as you feel comfortable, or until you start having problems.
If you don’t have time to do it right, when will you have time to do it over?
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Re: Chain Drive - Velocity & Accel Setting

Postby kevinl » Mon Feb 01, 2016 7:56 pm

thanks for the reply, so you've not move your x axis up to the 1000 in*oz motor..

this larger table and faster G0 & even G1,G2&G3 speeds as added a quicker response on my part. oh crap, things can go bad quickly.. the other night I was set up to cut a few diamond shapes in a 1/2" mfd, set z zero to the top of the spoil board, watch it air cut with z inhibited for 10 minutes. got brave and was ready to run the gcode with a 90 degree v-crave. press cycle start and things looked great across the first cut and the return cut at the deeper finish level, then thing when wrong.. forgot I had program CAMBAM to use .25" part travel clearance till the machine lower in the material and started travel at 80 IPM through the next g2 cut.. darn this is a lot different then 30 IPM.. it was a 3" or 4" cut before I could get to the E-stop..

I see at least two changes in my future, multiple e-stops are needed and a simulator will have helped...
kevinl
 
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Re: Chain Drive - Velocity & Accel Setting

Postby Awesomeness » Mon Feb 01, 2016 11:54 pm

Haha yeah, that kind of stuff happens. I have a checklist by my CNC, and the last step is something like "Press Cycle Start button. (Keep mouse positioned over Emergency Stop button, in case something goes wrong.)"

In the end, these machines shouldn't scare you much. The reason is that there isn't too much that can actually go CATASTROPHICALLY wrong... they just aren't powerful enough. You might break a bit, or bog out the router, or lose steps and have to start over, but there isn't much chance of actually breaking anything, or hurting people. I once screwed up a program on a big Haas mill, with a 20HP spindle, and it thought it was trying perform a tapping operation with a 1" drill bit! It grenaded the bit, while gouging out "chips" of aluminum about the thickness of my thumb, shooting shrapnel into the protective window. The machine didn't even lose position. Those machines are scary...
If you don’t have time to do it right, when will you have time to do it over?
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