Revolutionary Linear Drive System - Page 4

## View Poll Results: What is your prefered high precision linear drive system?

Voters
246. You may not vote on this poll
• Ball Screws

157 63.82%
• Rack And Pinion

33 13.41%
• Linear Motor

21 8.54%

22 8.94%
• Nexen's Roller Pinion System

12 4.88%
• Other

15 6.10%
Multiple Choice Poll.

# Thread: Revolutionary Linear Drive System

1. ## Re: Revolutionary Linear Drive System

If somebody was to provide the maths required to create the curve of the rack, and output it to a DXF, would people cut there own? Another thread on here discussed the cycloid gearbox and making your own. Seems people were very interested in that....and guys created a program to spit out the profile in DXF. I love the way the pinion is easy to make in this system.

2. ## Re: Revolutionary Linear Drive System

I already did that. I created an AutoCAD macro to create the rack profile, and cut a sample from Plywood. Then I decided to use helical R&P instead. I need to try to sell these roller pinions I have in my drawer.....

3. ## Re: Revolutionary Linear Drive System

I think if you apply an accumulation factor to any measuring device then provided the series of objects that make up the accumulated length each do not vary more than .01mm then the accumulated measurement overall will be very accurate indeed.

This means if you have rack sections 12 inches long and they were precision ground on their ends to within .001" each then who needs the expensive Nexen type R&P when your 20 foot rack would only be out by as little as .020" maximum......guaranteed.

I doubt that anyone (at home) has the capability to measure or check a measurement of 20 foot to within .020".....at the same time any work performed on such a machine would be accurate to within .001" for every 12 inches.

Many years ago I worked with an inside tubular stick micrometer that measured 2 metres in 600mm lengths....it had a calibration certificate from a metrology company that guaranteed the overall accuracy.

As that is an achievable factor, then a segmented rack will be in the same category provided the butted ends are in close contact.

It just means the pinion must make metal to metal contact (spring loaded etc) with the teeth tightly meshed in the rack to eliminate backlash......who expects to get that accuracy on a big DIY CNC router anyway.
Ian..

4. ## Re: Revolutionary Linear Drive System

I believe that the Nexen racks come in 1 meter lengths, with a jig to mount them with the correct spacing. They probably have a small gap between them.

5. ## Re: Revolutionary Linear Drive System

Originally Posted by ger21
I already did that. I created an AutoCAD macro to create the rack profile, and cut a sample from Plywood. Then I decided to use helical R&P instead. I need to try to sell these roller pinions I have in my drawer.....
Any chance I could get my hands on the macro? Never used one in Autocad so it should be fun. I did read most of the pages of the post, I must have missed that part of it.....

6. ## Re: Revolutionary Linear Drive System

I can't seem to find it. I may not have saved it when I got a new PC. Here's a drawing I created with it.

7. ## Re: Revolutionary Linear Drive System

Shame, that DWG doesn't help with the design of the rack, and the shape of the curve of the teeth. Thanks anyway.

8. ## Re: Revolutionary Linear Drive System

I used that drawing to cut a sample.
It just needs to be trimmed, as each tooth is a little long at one end.

9. ## Re: Revolutionary Linear Drive System

There are different sizes of Nexen rack and pinion, and this is only good for one size.

10. ## Re: Revolutionary Linear Drive System

The DWG that you sent has this;

That the pinion, not the rack....
So to get the rack, you rotated the pinion multiple times and took snapshots?

- - - Updated - - -

Ohhhh ****e...sorry I didn't zoom out.....

11. ## Re: Revolutionary Linear Drive System

So your macro rotated the pinion and took multiple snap shots to create the path of the teeth, and make spline with those co-ords. I guess you could have stipulated the "resolution". However, I think that this type of operation would not result in linear motion that is proportional to the amount the motor rotates.
That is because at this part of the curve;

the pin in the pinion is not moving at the same proportion as the profile of the tooth. I might be wrong, but I've seen this curve in cycloid gearboxes, and they don't provide constant velocity inside each revolution. I'll have a play with this and see what gives, much appreciated for what you have done.

12. ## Re: Revolutionary Linear Drive System

So your macro rotated the pinion and took multiple snap shots to create the path of the teeth, and make spline with those co-ords
It basically rolled the pinion, and tracked the center of the rollers. I don't remember the exact details. In the section you highlighted, the segment lengths are about .02mm.
I then offset this path by the radius of the roller, and converted the straight segments to arcs to smooth it out. It's not 100% perfect, but I think it's very close. It would have been fine for what I was going to use it for. It rolls very smoothly over the test rack I made.

13. ## Re: Revolutionary Linear Drive System

Nexen gives out the rack DXF on their site.

Ger21, you still have those roller pinions?

14. ## Re: Revolutionary Linear Drive System

No, sold them about 6 months ago.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•

We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!