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Davek0974
07-29-2014, 08:11 AM
I'm looking to redesign the floating z head on my CNC plasma table, currently using two ball bearing drawer runners but they were mainly proof of concept and are wearing out now :)

It needs very short travel (10mm) linear motion in a compact form with very little play or slop.

Looking at HiWin rail but it seems quite bulky for what i need, any excess displacement of the torch mount will eat into my usable Y axis travel.

Any thoughts?

RichR
07-29-2014, 10:23 AM
Maybe a block of acetal with two holes sliding on a couple of rods?

DICKEYBIRD
07-29-2014, 10:37 AM
Here's a link to a Darex grinder slide design I think is very clever. Wish I'd thought of it!
http://bbs.homeshopmachinist.net/threads/38473-Clever-folks-those-Darex-people-%28Linear-slide-pics%29?highlight=DAREX

DaveM 7766
07-29-2014, 12:20 PM
Take a look at these.
http://www.igus.com/drylin

dp
07-29-2014, 12:45 PM
Something like this, maybe. http://glacern.com/sbr

Bulk is a problem given the short stroke. I keep trying to find a project for these rails but haven't yet found one.

elf
07-29-2014, 12:50 PM
If the head weighs less than 6 pounds, then one of these stages may work: http://www.motionusa.com/online/shop/ball-bearing-positioners/3906--parker-daedal

The technology is similar to the Darex, but uses 4 rails with balls between them.

Similar items are on ebay quite often.

Paul Alciatore
07-29-2014, 01:06 PM
Maybe a block of acetal with two holes sliding on a couple of rods?

You won't get much more compact or inexpensive than this.

Davidhcnc
07-29-2014, 01:10 PM
Mount the head via two leaf springs similar to The Lauf fork. google it.

Then use a screw to drive down, spring return, you will figure that bit out. This will have no slop or backlash.

Use a steel rule for the springs and whatever clamp blocks you need to make to fit your application.

Davek0974
07-29-2014, 02:43 PM
Thanks all, I'm liking the acetal block idea and the lauf fork design, that one in particular seems ideal. If the torch was biased towards a fixed end stop, the z axis could drive into the surface easily triggering the stop switch and would retract against the end stop providing positive location of height.

It could be built with the torch inboard mounted and would then take up even less real estate than my existing design with the drawer runners :) Could possibly even build it around my z axis with the torch behind it! this would gain me possibly 100mm more Y axis travel, can't be bad ;)

kf2qd
07-29-2014, 09:25 PM
A small slide made from 2 aluminum blocks with some 1/16 music wire and some 3/16 ball bearings would make a very light but very free moving slide that has good dust tolerance. You can buy them or make them.

An acetal slide would rely on drilled/reamed holes and having everything perfectly aligned. And it would have low dirt tolerance. Plasma is a dirty operation.

http://i250.photobucket.com/albums/gg244/kf2qd/Slide1_zps3ffba51f.png (http://s250.photobucket.com/user/kf2qd/media/Slide1_zps3ffba51f.png.html)
http://i250.photobucket.com/albums/gg244/kf2qd/Slide2_zpsace79797.png (http://s250.photobucket.com/user/kf2qd/media/Slide2_zpsace79797.png.html)
Inner and outer slide from aluminum (or aluminium...)
rods from 1/16 music wire. Brass or steel for the adjustment plate.
And a plate or 2 on the top and bottom of the slide and frame to keep everything in place.
And a brass or plastic (from coffee can lid) spacer for the ball bearings.

Thomas Staubo
07-31-2014, 03:42 PM
In the thread referencing to the Darex slide, there's this picture of a radial arm saw slide:

Where can one buy these, and what are they called?

http://img.photobucket.com/albums/0803/jstanley/dewaltrollers.jpg

macona
07-31-2014, 06:48 PM
Make it from some maker slide:

https://www.inventables.com/technologies/makerslide

Davek0974
09-21-2014, 07:31 AM
Finally found some spare time to mess about with the new floating head. In the end I went with the Lauf fork idea, it seemed a good one and I think it will work great.
http://www.davekearley.co.uk/LinkPics/FH1.jpg

Had to mess about with the springs, started off with some steel rules cut down, they're springy and 10apenny on eBay, this was way too stiff, almost solid. This version has four 0.006" feeler gauge fingers as the leaf spring elements, much better - just the weight of the moving portion and the torch now, if that's too heavy I can lighten the front plate considerably.

The best part is that there is absolutely zero backlash or twist etc, it's very flexible up and down but totally rigid in all other directions.

Thanks for the suggestion.

Glug
09-21-2014, 11:16 AM
The best part is that there is absolutely zero backlash or twist etc, it's very flexible up and down but totally rigid in all other directions.

That's neat! There is lotsa elegance in something so simple. You also don't have any sliding surfaces to wear, lube and keep clean of debris. Replacing the springs will be trivial and dirt cheap. Another bonus is not needing to order specialty components and waiting for the post in order to build it - there is a lot to be said for the satisfaction that comes with walking out in the shop and making it happen.

It looks like it must have lateral deflection as it moves vertically. I suppose that is not a major concern because of this particular application; flat workpieces, and only 10mm of Z travel.

brian Rupnow
09-21-2014, 01:33 PM
Guys--for any type of rolling guide, google Bishop Wisecarver. they make some great roll/slide mechanisms and sell parts.---Brian

J Tiers
09-21-2014, 01:51 PM
That feeler gage system is good. It DOES move the "carriage" in and out as well as up and down, but that may be inconsequential for small movements. And of course it is for a plasma cutter, so the need for precision isn't what it might be for laser or water jet cutters.



In the thread referencing to the Darex slide, there's this picture of a radial arm saw slide:

Where can one buy these, and what are they called?

http://img.photobucket.com/albums/0803/jstanley/dewaltrollers.jpg

I'll bet that is my picture, the carriage bearings from a DeWalt radial arm saw.

I think I got bearings from a bearing house for it.... if so, they had of course to be ordered. But I MAY have gotten them from a place specializing in radial arm saw parts.

Davek0974
09-21-2014, 01:53 PM
There is some lateral movement of course but, as the total movement needed is only about 4-5mm and the fact that when the torch is cutting it will be resting against a fixed stop, the microscopic amount of lateral shift will no difference at all.

If the probing height changed each time then it might make a tiny difference but it's a fixed distance from torch tip to the height switch so hopefully it will work fine.

The torch is mounted inboard of the front plate so between both plates, this keep the torch really close to the z axis which increases my table real-estate too.

A crash will likely booger the springs but as said, they are easy to replace.

Norman Bain
09-21-2014, 04:39 PM
If you are getting thru lotsa those flex springs consider supply of spring material from metal pallet strapping.

It comes in various widths and can be had in great quantity for zero cost.

Cheers,
Norman

Davek0974
09-22-2014, 12:08 PM
Here's the finished version, ready to fit, rest stop is combined with the trigger finger, neat and tidy.

I lightened the front a bit as well.

http://www.davekearley.co.uk/LinkPics/fhead.jpg

Should bolt straight on.