Turcite vs Moglice vs Delrin

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Hi,
I have been toying with the idea of making a 2 1/2D cnc router to cut out ribs etc for model airplanes. My thoughts for the slides were hovering around lengths of ground ms bar, the saddles being cut from box-section ms having holes
drilled for plastic bearing bushes. I've read around and am trying to determine whether Turcite or Moglice or Delrin would be suitable for the bearing bushes ? I have found Delrin readily on eBay but I know the other two materials are specifically intended to be used in bearings, can anyone say which of these is best in this kind of low load application, and whether the advantages outweigh the convenience of Delrin ? Also a supplier of small quantities in diameters between say an inch and half an inch would be helpful.
Many thanks,
--
Boo

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On Mon, 27 Nov 2006 17:48:28 +0000, Boo

Have you considered Glacier DU bushes? They're a steel/bronze/PTFE composite, I haven't used any for donkey's years & don't know if it's available now in standard sizes from the usual bearing houses but it might be quite good for that sort of job?
Tim
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On Mon, 27 Nov 2006 18:04:42 +0000, Tim Leech

Or how about Oilite bushes? Cheap and readily available. Or buy a length of leaded bronze and make some - I made the leadscrew bearings for my ML7 from this.
Peter
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Tim Leech wrote:

Excellent things DU bushes, every modern car would be lost without them. If you've got a car breaker local, bludge a couple of front suspension struts off him. That will give you good lengths of hard chrome bar and DU bushes, all good stuff for your router table. As cars come in various sizes so do the struts.
Tom
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I would seriously consider "ball bushing" bearings or whatever ball bearing type linear slides are around on ebay etc, plain bushings of whatever type are troublesome in the long run- I talk from industrial and home experience-alternatively computer printers are a source of this type of slide-good finish bar if bushes not salvageable, any independant computer dealer will have loads, as will your local council tip-but that is a case of dealing with jobsworths ( or bribes !) Mark G.
wrote:

out ribs

around
having holes

determine
bushes ?

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Mark G wrote:

Your experience obviously doesn't include DU bushes.
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Er.. well yes my experience does include DU bushes from 8 mm to 50 mm bore, they are good, but if you can get a ball bushing or other ball based linear slide cheap you will be on a better route to success.-Does any decent machine tool use otherwise ? DU bushes are esentially a leaded bronze bush with a ptfe coating,steel backed, great when new, but will not withstand well to intermitent side loads such as in a machine slide. Mark G.

bearing
type
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Mark G wrote:

They also can have some stiction compared to rolling element linear bearings.
I used to use 1000's of 3/16" DU bushes on an instrument job I was involved with. We found we had to burnish the bushes to stop it. The shafts were mirror polished stainless steel.
My recommendation for CNC use especially when using stepper motors is the lowest friction bearing you can find.
Wayne...
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Wayne Weedon wrote:

You blamed the bushes for the stiction? LOL
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Tom wrote:

LOL Indeed. Do you think we didn't research the problem? This was a very low force application <10g. Nevermind clever clogs you obviously know more than the application engineers that helped us resolve it.
But back onto subject DU's have no real place in this application.
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Wayne Weedon wrote:

Obviously more than the designer who did the original specification. I've been using or specifying either Glacier or INA bushings and wear strips over 25 years, for units moving from 1 pound up to 10 tons, without having to resort to "application" engineers to create a workaround for a design fault.

Says you... Based on one experience. I suggest you acquaint yourself with the INA Permaglide product application range.
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Tom wrote:

You know I didn't notice you there 15 years ago when this happened, maybe you were hiding in the closet. But I can assure you it was designed to the glacier recommended parameters.
Tom each application has it's vices, what works well for one application may not work so well for another. In this case the instrument had very low internal force available to return the shaft to it's zero position. In the end it was made to work and well. But not quite so easily as Glacier said it would ;)
But it's History now, and I'm glad I've moved on.

No based on my cnc experience. No commercial machines that I know of use DU's and rarely do they use round linear ways except on the cheapest hobby machines. They just don't lend themselves to the rigidity required.
There are tons of surplus linear motion items available on ebay etc, and the original poster might want to look to see whats available rather than re-invent wheels.
I've seen lots of people get very annoyed and frustrated when their homebrew cnc's don't perform well.
All my cnc milling machines use box ways, and bonded on Turcite as well as automatic lube systems. I've used more modern machinery with bolt on linear ways, and although nice and fast. SUCK for rigidity in many cases.
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Wayne Weedon wrote:

Wayne, the OP only wants to cut out ribs n stuff for model aeroplanes, most probably 20g tops...
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Tom wrote:

Yes Tom I saw that. But having been around a lot of people doing homebrew retrofits as has J.S. I have seen so many start off saying "I only need this" But later wish they had made the machine to be capable of doing "That" !
Same with the size issue!
Sadly reading through the posts on some of the CNC forums, there is quite a lot of frustration. Most of which could of been avoided with a little time spent earlier on planning the thing out.
Wayne..
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wrote:

This one does.
http://web.onetel.com/~duttondock/Pictures/Ward-1.jpg
OK, I realise you probably meant current CNC machines, & this one is neither current nor CNC. I just thought I would throw it in to be mischievous. In fact it may well predate Turcite, Moglice etc., I don't know when they became readily available?
Cheers Tim
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Tim Leech wrote:

Hehe.. Yes not CNC. I've seen an used a fair few Ward Capstans. But what the hell is that thing? I'm intrigued. Looks more like a t&c grinder?.
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wrote:

Yes it is a controlled spiral cutter grinder, will grind spiral flutes without the use of guide fingers as well as all the usual T&C functions. Made by Ward Grinders in Dorset, spiral grinders were their speciality. No connection AFAIAA with the other lot.
Cheers Tim
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Tim Leech wrote:

Tim
I actually thought after I posted that maybe it was a product of Ward Grinders in Parkstone, Poole. I have quite a few friends in the business who served their time there. Maybe some of them worked on your machine.
Long gone now I think.
Wayne...
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Just to throw another oar in the water here.
I have had two personal experiences where the ball bushings were replaced by the plastic lined bushings from RS and worked better. Both were low force applications and both had problems with fine dust.
One was on the Y axis of a laser cutter and the fine dust and fumes caused the ball bushing to tighten up in service. Once on a service call we couldn't get any new bushings locally in time and replaced them temporary with some RS lined bushes whilst spares were ordered. They never got fitted as the lined bushes wiped the shaft clean and it ran until it was scrapped a few years later.
Because of this experience I swapped the ball bushing on a CNC router for lined bushings as the MDF dust was having the same problem and again it cured the problem.
With better designed seals and covered bellows on the way the ball bushings may have been no problem but with the skeletal build up of both these machines the lined bushes cured what problems we had.
. -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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John Stevenson wrote:

Yes a problem with round linear rod is that need to support it, and therefore the slot required through the bearing to clear the supports.
It is one of the reasons I dislike them. The longer the travel you need the worse the problem seems to get. As well as their need to be elevated over any solid base.
Those NSk(etc) linear rails at least can be bolted down onto a flat surface. I do realise there's a cost issue with those though ;) There are bargains to be had if you look hard enough.
Wayne...
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