# Acme screws versus rack and pinion drive



## RainMan 2.0 (May 6, 2014)

*Acme lead screws versus rack and pinion drive*

Guys I wasn't aware there were differant options for the stepper motors to move the X and Y axis on a CNC router table .
I'm assuming steppers attached to a rack and pinion drive would be more accurate than steppers connected to acme lead screws . 
Any disadvantage to using the rack and pinion drive other than cost ? 
I was thinking that since the stepper motors stay stationary with the acme screw system that there wouldn't be a need for extra wiring moving along with the gantry as with the rack and pinion . At least that's what I'm thinking, but I'm not very familiar with these options yet


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## RMIGHTY1 (Nov 5, 2014)

Hi Rick, here is what I found on the subject. I had read about this before but forgot it all. 

http://www.cncrouterparts.com/which-is-better-a-screw-or-rack-and-pinion-drive-p-99.html

This should be a good start.

Enjoy my friend!!!


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## jw2170 (Jan 24, 2008)

Good question, Rick.

I guess there may be a reason why acme thread is so popular.


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## honesttjohn (Feb 17, 2015)

Rainman,

Looks like R&P for you, since you'll fill up a whole garage sized space by the time you get done.

I can see it coming.

HJ

Just pull the trigger - you know you're going to


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## RainMan 2.0 (May 6, 2014)

RMIGHTY1 said:


> Hi Rick, here is what I found on the subject. I had read about this before but forgot it all.
> 
> Which is better, a screw or rack and pinion drive? | CNCRouterParts
> 
> ...


That's about what I thought , the only down side is more cable management with the R&P . Not a big deal really .
Thx Ray , good find


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## RainMan 2.0 (May 6, 2014)

honesttjohn said:


> Rainman,
> 
> Looks like R&P for you, since you'll fill up a whole garage sized space by the time you get done.
> 
> ...


Yes I'm seeing the reasoning now . What I'm really liking is the fact that if you use R&P that you can build a 4'/4' table and then add at a later date if you find it to small .
Although I really want a 4/8 and be done with it


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## honesttjohn (Feb 17, 2015)

How much more expensive is it to get the 4 x 8 table? Can you get the parts and have them ready to add while using a smaller piece of the bed to get started? Just asking. 

I would think buying all the parts at once and making one trip would be cheaper than redoing it all later, especially if you can get up and running with a smaller bed to start.

That's why I got the rotary and the big bed with mine. Don't have a clue when (if ever) I'll use it all, but it fits the machine and it's there if I ever need it, and was a little cheaper being included in the package.

HJ

Business basics are the same, no matter what the product


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## Cherryville Chuck (Sep 28, 2010)

The steering in your vehicle is rack and pinion Rick and the pinion gear wears the fastest being the smallest most active part. Just like the steering in your vehicle can get loose as it wears so would this I would think.


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## bgriggs (Nov 26, 2008)

I have been using Rack & pinion for about 5 years. I would not go back to leadscrew. My machine is faster, requires less maitenance and actually cost less.

Bill


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## RMIGHTY1 (Nov 5, 2014)

bgriggs said:


> I have been using Rack & pinion for about 5 years. I would not go back to leadscrew. My machine is faster, requires less maitenance and actually cost less.
> 
> Bill


Wow, that is a great endorsement Bill. Thanks (not that I am getting a CNC machine but appreciate your valued input).


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## Cherryville Chuck (Sep 28, 2010)

Have you noticed any change in accuracy over time Bill?


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## MEBCWD (Jan 14, 2012)

honesttjohn said:


> How much more expensive is it to get the 4 x 8 table? Can you get the parts and have them ready to add while using a smaller piece of the bed to get started? Just asking.
> 
> I would think buying all the parts at once and making one trip would be cheaper than redoing it all later, especially if you can get up and running with a smaller bed to start.
> 
> ...


John,

On a 4x8 bed, if most of your projects are small , say fit in a 2x2 area, You can set up 6 more projects while one is cutting, then move from project to project so you save time by being able to start cutting on the next project. If your projects fit in a 2x4 area then you can set up 2 or 3 more jobs while the current job is running. If your jobs fit a 4x4 area you can have the next job setup and waiting.

The exception to these is the use of the full 8 foot length(like 2x8 area) of the bed because the gantry would be in the way unless the cutting is rastering across the bed but you need to know when the you can work in the open part of the bed and I would not recommend it if the toolpath might change when you least expect it.

I wish I had the room for a 4x8 bed in my shop.


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## honesttjohn (Feb 17, 2015)

Wow, Mike !

I never thought of it that way. I'm still basking in my 11" - 4 letter name plate (with a space and period, I might add). That makes a lot of sense, or should that be cents.

Thanx for the insight.

Go for it RainMan !!! Get the big one !! We approve !! 

HJ

Not as smart as he thought


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## Seaorsaw (Mar 8, 2015)

cncrouterparts has nice kits for 2x4 and 4x2 and up...rack and pin.... you can add to a smaller kit later and use most of the parts for a larger one,,,4x8. They have a standard version and a pro version... ( thats why 2x4 and 4x2) Also some tabletop versions which look very heavy duty for metal...


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## RainMan 2.0 (May 6, 2014)

RMIGHTY1 said:


> Wow, that is a great endorsement Bill. Thanks (not that I am getting a CNC machine but appreciate your valued input).


Yes I was hoping Bill was going to pipe up 

Ray I'm with you , it would probably best to do it once . Just not liking the real estate in my garage l but if there's a will there's a way .
I'm really liking this kit concept .


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## bgriggs (Nov 26, 2008)

Cherryville Chuck said:


> Have you noticed any change in accuracy over time Bill?


No I have not noticed any changes. However The pinion gear is a wear item that will need to be replaced after a few years. 

Bill


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## RainMan 2.0 (May 6, 2014)

Ok one more thing I haven't figured out is why are there electronics for a 4th axis ? Is the 4th axis for an additional option that turns the object on the bed ?


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## honesttjohn (Feb 17, 2015)

Wouldn't the 4th axis be for a rotary? That's what it is on the Probotix.

It's probably there just to confuse you, Rainman. lol

HJ

Has almost as many axis as fingers.


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## RainMan 2.0 (May 6, 2014)

honesttjohn said:


> Wouldn't the 4th axis be for a rotary? That's what it is on the Probotix.
> 
> It's probably there just to confuse you, Rainman. lol
> 
> ...


I think you called it John . I wonder if a guy could justify getting that option . Guess it all depends on what you like building.

I wonder if you had a 3D scan of an object , if there's software so the router could turn the piece and make it . That would be cool and worth the upgrade


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## Seaorsaw (Mar 8, 2015)

RainMan1 said:


> Ok one more thing I haven't figured out is why are there electronics for a 4th axis ? Is the 4th axis for an additional option that turns the object on the bed ?


Both sides of the gantry are driven by a motor on some machines, so one is x and the other is x' or sometimes called A as the slave of x. So you need Y and Z... 4
So they call it 4 axis because it uses 4 drivers for the motors


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## honesttjohn (Feb 17, 2015)

I got it. Won't probably ever use it, and much much later on if I do. Look at it as a "fancy" lathe. If you get pretty proficient on the regular machine, you may want to venture a little further into the abiss. Or, there might be a project where you need it for that added touch. I say, get it all at once, so the parts all work with the same setup. You know how quick they change things. They might even make you a sweeter deal.

I hear you can do some wild stuff with Aspire and Vcarve Pro. It's learning that damn programming thing.

HJ

Big fan of "plug and play"


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## RainMan 2.0 (May 6, 2014)

honesttjohn said:


> HJ
> 
> Big fan of "plug and play"


I'm with you on the plug and play but it sure comes at a price . I'm not sure what Scott ordered but there is a wiring setup from this company that takes most of the guess work out of it I believe .
I can certainly read schematics and use a soldering iron , but at this point I think I'd sooner just plug in the appropriate jacks and keep the soldering and guess work to a minimum

With my luck I'd cross the wires and each side of the Gantry would move the opposite direction . That would be the end of the game I believe as it warped itself to oblivion


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