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Author Topic: Setting up a 4th axis?  (Read 11510 times)

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Offline Chip

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Re: Setting up a 4th axis?
« Reply #20 on: July 05, 2008, 11:09:21 PM »
Hi Dave

At least you'll get your feet wet.

Let us now.

Any-Time, Chip

Offline docltf

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Re: Setting up a 4th axis?
« Reply #21 on: July 05, 2008, 11:58:35 PM »
DAVE

if you go with that 30-1 reducer, then you need to do another gearing of 1.5-1 so you can put your degrees on whole numbers. this is very important to using a rotory and mach3. so 30-1 X 1.5-1 X 200 =9000 fullsteps.
9000 divided by 360 gives you 25.0 steps. when you make your base set up like this mach3 likes it. then if you go microsteps you won't have problems. when you do rotory steps that calculate to numbers like 11.667 and 14.22333
at whole postions 1 degree or .5 degree you got trouble. you wan't to see numbers like this in key spots 0.00  0.05 0.025 0.5 12.5 then if you microstep at 1/2 1/4 1/8 you will gain resolution and solid numbers for mach.

bill

Offline Chip

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Re: Setting up a 4th axis?
« Reply #22 on: July 06, 2008, 02:38:00 AM »
Hi, Bill  :D

Not trying to split Hair's hear, There some part's that Dave has sitting around, Now, On Hand.

6000, 11.666666 steps per, You get some rounding, .0143 .02 .03 deg, 12.5143.  ???

Even with 9000, 25 steps per, You'll still get some rounding, .02 deg. 12.5 is shown as 12.4800.

Now 7200, 36 steps per, seam's good, So dose 1440, 7.2, 144000, 400 steps per.,Hmm.....360 ?

73400, 367 steps per, 12.4986.

NO Hair Splitting Allowed, Chip  :D

PS: PI are round, Cornbread are square.  :-\

Offline jimpinder

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Re: Setting up a 4th axis?
« Reply #23 on: July 06, 2008, 03:11:58 AM »
I can't understand all this.

Can you get a 36 to 1 gearbox - then all your theory is solved and all the sums cancel out. There are 360 degree in a circle - why bother with 30 unless you are forced down that road. Failing that, put a 5 to 6 step down between your motor and gearbox, using toothed pulleys - say using 10 to 12 teelth pulleys - this will also cancel out your 30 ratio gearbox and give you a simple figure of 36 on which to calculate steps per degree - and enough has been said about that in the past.

Hood - in my experience there is no backlash in modern toothed belts - look at car timing belts. The only error is that particulary tooth having a little bit of play with the corresponding gap in the belt, but since there are many teeth in contact with the belt, the resultant movement is non-existant
« Last Edit: July 06, 2008, 03:15:56 AM by jimpinder »
Not me driving the engine - I'm better looking.

Offline docltf

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Re: Setting up a 4th axis?
« Reply #24 on: July 06, 2008, 05:29:13 AM »
HI CHIP

Budman want's to do a rotory and i believe he said that his experiance with this is slim to none. he also mentioned that he is going to work with dia from .250 to 2.0 .which we both know is bogus, because as soon as he gets it working well
he will put somthing bigger in it the first chance he gets. we all do! but .250 to 2.0 is a good place to start. plus Budman has not mentioned if he has microstepping available. if he does it will be better for him. he also needs to know that larger
dia needs more resolution and more resolution means less speed. he just needs to have some info for his first build. how he plans to build and with what is his choice. i just want to give him something to think about.

Chip i diddled with your doodles.
6000=16.66(20 more)7 steps per
7200=20 
1440=4  i built one of these works pretty slick
144000=400 that's good

what i was trying to show budman about a good base setup and mach3 and if he has microstepping how it works out
if he builds with the 30-1 does the 1.5-1 gearing and 200 full step pulses, he will get 360 in 9000 pulses. that is 25 pulses per degree.
these numbers will be available as degree's on the DRO'S without rounding  1.0 2.0 3.0 etc.
now lets microstep.
F step 25=1.0 2.0 3.0
H step 50=1.0 1.5 2.0 2.5
1/4 step 100=1.0 1.25 1.5 1.75 2.0
1/8 step 200=1.0 1.125 1.25 1.375
1/16 step 400=1.0 1.0625 1.125
1/32 step 800=1.0 1.03125 1.0625  (mach3 DRO will round 1.03125 to 1.0313) but the number is still good.
these numbers show without rounding as the pulses increase.
doing big resolution with microstepping is kind of phony anyway,but it makes the DRO look good. big solid resolution is done with gearing.

P.S. my cornbread comes in round pie pans.

bill

Offline budman68

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Re: Setting up a 4th axis?
« Reply #25 on: July 06, 2008, 07:42:42 AM »
Bill, thanks for helping out and yes, I do have microstepping. As for doing any larger work, unless I win the lottery, and get more room available to me to buy a bigger machine,I don't think that's going to happen anytime soon!  ;)  I do know exactly what you meant though..it just often works out that way doesn't it?

Jim, I possibly might be able to get this gearbox very cheaply so that's why I threw that into the equation, but I'm thinking more and more about the sherline, and that may be the road I'm headed down eventually because it does seem "dumb" to go that way if I just wait a little longer to buy it. Seems like a really well built unit and I'm only hearing great things about it. Can't argue with success.

Again fellas, thank you for your input, I've already learned quite a bit and I haven't even started building this up yet. As Bill mentions, I know slim to none about this area, and that's why I came to you.

P.S. I LOVE Cornbread in any pan!!  ;D
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Dave->    ;)

Offline RICH

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Re: Setting up a 4th axis?
« Reply #26 on: July 06, 2008, 08:46:11 AM »
- What kind of backlash can I expect from the Sherline? -

Mine has approx 5 min and it varies a little. I always rotate it to take it out before indexing. You can use the backlash compensation
in MACH ( haven't tried it for a rotary table / should work fine ) and if your using a SS backlash compensation is not available yet.

I have not checked accuracy of the gearing as it's very time consuming, not worth the effort, and you need the right equipment to do it. Have done some checking of my Klinger table but that's a different story on how and why it was done.

Maybe someone will post some experience on engraving / machining around the circumference as it relates to a rotary table and what they found to be desired. It all depends on what your going to do with it.

RICH



 

Offline budman68

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Re: Setting up a 4th axis?
« Reply #27 on: July 06, 2008, 10:06:05 AM »
Excellent, Rich, that's not too bad at all.  -  :)
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Just because I'm a Global Moderator, don't assume that I know anything !

Dave->    ;)

Offline Chip

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Re: Setting up a 4th axis?
« Reply #28 on: July 06, 2008, 05:00:40 PM »
Hi, Dave

My Sherline works very nice, Great value, Didn't think you wanted to split hair's, Just wanted to get something running.

Thanks, Chip

Offline RICH

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Re: Setting up a 4th axis?
« Reply #29 on: July 06, 2008, 05:07:35 PM »
Dave,
I posted some pictures in show and tell. The "save good junk" is a picture of an extra mounting. Should you decide on a Sherline and want some good junk, for the price of postage you can have it.
 :)RICH