Turcite vs Moglice vs Delrin

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,
Reply to
Boo
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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
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Reply to
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
Reply to
Peter Neill
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
Reply to
Tom
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.
Reply to
Mark G
Your experience obviously doesn't include DU bushes.
Reply to
Tom
Can't help on the bearings, sorry. But ground bar can be very expensive. I was looking for some a while ago for an overarm for a milling machine. I ended up buying hard chromed bar from a hydraulic ram supplier.
How is the router itself 2 1/2D? Manual Z? Isn't that limitation only imposed by the CAM you use?
Reply to
John Montrose
try this guy
formatting link
I brought a couple of things from him
usual disclaimer
Andrew
Reply to
Andrew Bishop
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.
Reply to
Mark G
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...
Reply to
Wayne Weedon
You seem to be missing the point (as does everyone else) that Moglice is cast in place in a housing (it's mixed up like an epoxy) so getting the perfect fit is easy. It does suffer with high initial friction but the bearings bed in after a few cycles (in my experience). One thing to watch out for is that they don't get exposed to heat, we found that they tend to flow at >70C causing them to seize up (found during an elevated temperature storage test). Martin
Reply to
Martin Whybrow
My Ward T&C grinder has DU slides
Tim
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Reply to
Tim Leech
You blamed the bushes for the stiction? LOL
Reply to
Tom
LOL Indeed. Do you think we didn't research the problem? This was a very low force application
Reply to
Wayne Weedon
My old Summagraphics A0 pen plotter had a stepper driven head, and ran in plain oilite bushes on a ground 10mm shaft about a metre long. Did a fair bit of mileage in the 13 years I had it and a few more in the years before that. Still plotted perfectly with no stiction.
Designed and built a few cutting machines for mirror lens that we moulded, and used plain bushes on a ground shaft too, in use everyday since 1996 and still going strong as far as I know. Ran via pneumatic & hydro-pneumatic motion rather than steppers though.
However, I can't disagree with you about using the lowest friction bearings wherever possible, and linear ball bushings aren't that expensive now, and neither is hardened and ground shafting.
Peter
Reply to
Peter Neill
The job I was talking about was a linear displacement transducer. Before use DU's the bearing was just the brass body of the instrument. This was broached to the correct diameter, which gave a fantastic action, but was expensive. Like you said can last a long time, I remember an instrument coming back for service after 15 million full stroke cycles (10mm) measuring Weetabix boxes! It was as good as new.
The DU's were a cost cutting exercise, and once the problem was resolved it was perfect, but not as long lasting as the plain bearing.
Especially with steppers, they are rather sensitive devices. I tend to use servo's on my CNC's when I can.
Wayne...
Reply to
Wayne Weedon
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.
Reply to
Tom
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.
Reply to
Wayne Weedon
Wayne, the OP only wants to cut out ribs n stuff for model aeroplanes, most probably 20g tops...
Reply to
Tom

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