Thread: Linear Motion , CHEAP!!
Totaly new to this so pass a few ideas by you lot and see If they are good or crap!
Building a fairly big CNC for wood working so need a large bed size
In a perfect world 10ft x 5ft I do have the space in the workshop for that
BUT a bit over optimistic for my first attempt LOL so 5ft long x 3ft wide
With hopefully 2ftx4ft working area for MK1
The bed or base will be kitchen cabinates with a strong top as I am a cabinate maker
and so thats very easy for me to make
But the linear slides ,,, HUMM
Seen the skate berings and ali angle thing ,, works but
The V grove berings are better but at more than £12 each !!
Proper suported rails ECT is out of the question at the lenths I need
SO been brain storming and come up with ....
An aluminum I section thats 54mm x 25mm that has a 6mm hi x 4mm wide rib on the 25mm face running right along the lenth
I could use the skate berings in a V on ali angle , but its ugg ugg
I could use V berings but at £12 quid each and hardened steel on ali
would not last very long !
So skate berings with tyers? , replaceable nylon tyers
Ant thoughts or sugestions
Problem with using nylon wheels, is you risk losing rigidity due to flex in the wheels.
I wouldn't worry too much about running hardened bearings on an alloy extrusion. Provided you keep them clean and spinning, you shouldn't experience any major wear. You're only likely to experience major wear if things start sliding.
So unless you enclose all the running gear in bellows you will embed dust to the tracks/bearings that will give very stiff jerky movement.
Very expensive are bellows and awkward to implement.
28-01-2011 #4skate berings with tyers?
the tyres (+ the larger diameter) would smooth out any of the smaller rail inperfections
might be a winner if your after saving the brass
its allways a gamble though when you try something new
chris, have a look at "routercnc" build log, looks like he is running plain bearings on alli profile, looks like a winner :)
he seems happy with it anyway
Hi C Cunningham,
As Mark points out I am running bearing races directly onto Ali profile, but I always knew it was a short term solution and a small witness mark is appearing on the profile where the bearing runs over it. Not the best long term solution, although a hardened running strip might give better service.
Stray dust and chippings do get engrained on the top ali surface, and aligning the whole gantry (90 deg to bed, same height from bed at each each etc) took some fiddling. Once the extractor shoe is working that should solve the dust problem. The top and bottom bearings are fitted to short axles which run in adjustable slots in the side pieces. This allows complete alignment adjustment vertically. Side to side location is from single bearings set into holders, with one side fixed and the other side on an adjustable pressure plate. A bit like these :
Linear motion, cnc and cheap are a difficult combination.
28-01-2011 #8Linear motion, cnc and cheap are a difficult combination.
I had promised my self not to post untill I actually start building again, but maybe I have an idea that might be worth exploring.
If the machine was solely for woodwork and the correct feeds and speeds could be achived with the rest of the system, then surley the loading on the bearings could be reduced and then a small nylon or delrin "Tyre" wouldnt be such a bad idea and allmost a cheap throw away maintainance part if wear occurs. (it could even have a rib that runs in the profile channel to proved some lateral restraint)
If the section was thin enough it shouldnt compress to much and if it was made wider than the bearing it could spead the load over a wider section on the ali profile.
Im not saying that it is a perfect solution but for this application and accuracy I'm sure it would be worth a try.
28-01-2011 #9(it could even have a rib that runs in the profile channel to proved some lateral restraint)
that alli profle is pretty accurate, it sounds like it would work a treat
i cant see acetal/delrin wearing a grove in your alli to quickly
with the price of skate bearing being the way they are id be tempted to use two on each wheel and make the wheels as wide as possible
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