DIY Linear Bearings

[CraftyGeek]

I have it in my head that i'll use supported rails now...I know that its worth the extra pennies. Looking at chucking a load of old hobby bits on ebay to help with the funding.

I had previously been planning on using steel box - I think we exchanged messages about it ages ago.
I like the convenience that ally profile offers - I also have concerns about getting a frame built with steel box square...although since looking at the supported rails I did think it could be easier to attach them to a frame made from box rather than profile.

On the subject of rails, for a 2'x4' machine, what size rails would you recommend?
I've just been reading a load of build logs & have seen mention that 20mm is overkill for a machine this size & that 16mm may be a better fit...but then there were comments about the bearing size being harder to work with - found it all a little less than clear :-p

[birchy]

Personally, I really dislike the aluminium profile sections as they always feel a bit flimsy. I guess I've always made things in steel, so associate weight with strength. Your frame doesn't have to be perfectly square, it's the rails that have to be parallel and square to each other. The framework could easily be a couple of mm out of square and you'd still be able to build an accurate machine if you mount the rails correctly.

[JAZZCNC]

I had previously been planning on using steel box - I think we exchanged messages about it ages ago.
I like the convenience that ally profile offers - I also have concerns about getting a frame built with steel box square...although since looking at the supported rails I did think it could be easier to attach them to a frame made from box rather than profile.

What makes you think you'll get it any squarer using Profile than steel.? To be honest it's actually harder to get and keep square than steel.!
With steel (presuming your welding) it's just case of tack it up knock square then when happy finish up the welds while keeping eye on it moving. After that it will never move again.
With profile your messing around with corner diagonal braces and shims etc then first time you move it or shaking thing about a bit while cutting it's moved again.!!!

Like Birchy says with steel it's strong and doesn't need to be micron square. The rails are what matter and steels much more workable than profile so more flexible regards alignment etc.

By the time you have bought the profile and all the T-nuts etc which can cost has much has the profile you'll be into £200 plus with steel you'll do it for £60-80 and still have some left. That's £150 towards your rails.!!!

Meant to ask this before.? What you doing regards screws etc . . Your not thinking threaded rod are you like lots of DIY rail folks do.?
If so then again don't waste your time and go straight for balls screws and get them at same time has rails to keep costs down £300-£350, can get you a set of rails and screws with all end fixings and machining. Wouldn't or Don't even consider Lead screw has again it's not worth the small difference ballscrews cost.
You'll have a proper machine that can do some serous work all day long and will be worth at least double the cost you put into it if done right.

Steel is the way to go IMO Esp if your on budget. Profile looks bling but that's about the only thing it's got over steel all the rest that matters it's behind on.!!

[CraftyGeek]

Ok - so it looks like its about turn time & back to the drawing board.
Are we talking 50mm x 3mm mild steel box?

It'll be bolted, not welded as I don't have the gear for that - but I do have a pillar drill & some taps, so should be able to cobble something pretty sturdy together.

Screws - i was looking at a Marchant Dice package on ebay...but given that i'm now looking at supported rails from Chai, i think it makes sense to get some screws from him as well - i'll need to look at what he offers & the pricing. If the steel does work out that much cheaper, then the budget shouldn't be an issue.

I'll call my local metal supplier tomorrow to get a quote for the steel box & then start drawing something up.

[irving2008]

Also, if you're following that design..... don't... the single central screw for the X-axis will cause you hours of pain if you plan to cut anything stronger than cheese at the full width of the Y axis. Plan and budget for two screws and either 2 drives & motors or a single motor and pulley system unless you make the x-axis bearings really long to counteract racking. Go re-read some of the build logs, its been discussed in depth many times. If you're investing in a serious machine, best to get it right at the outset!

[JAZZCNC]

Also, if you're following that design..... don't... the single central screw for the X-axis will cause you hours of pain if you plan to cut anything stronger than cheese at the full width of the Y axis.

While I agree completely 2 screws are best route in this case it's marginal Irving has he only wants 600mm cutting width, if he has wide enough bearing spacing on X axis and builds ridged Gantry it will be fine for upto light Aluminium work. On a budget this will work fine and with bit of thoughtful design could easily be incorporated later if needed.!!. . . . .Carry on Sir I say.

Are we talking 50mm x 3mm mild steel box?

I'll call my local metal supplier tomorrow to get a quote for the steel box & then start drawing something up.

Yep 50 x 3mm and the last time I bought some which was 2-3months ago it cost me £26 for 7.5mtr length. That's was plus vat but if like my friendly supplier they will some times do without Vat.

[irving2008]

While I agree completely 2 screws are best route in this case it's marginal Irving has he only wants 600mm cutting width, if he has wide enough bearing spacing on X axis and builds ridged Gantry it will be fine for upto light Aluminium work. On a budget this will work fine and with bit of thoughtful design could easily be incorporated later if needed.!!. .

Ok, on that width maybe you're right, but in that case the X bearing spacing on that design is nowhere near wide enough IMHO, so don't underestimate the extra X travel length.

[CraftyGeek]

Cheers chaps - My original plan was to build it using a single x-axis screw...see how it goes then add a second at a later date if I feel I need it.

I'm now ditching the FLA-100 as a base design & am starting a new design from scratch with 50mm box.

My local supplier states £4.10/m +VAT as a base price, then depending on quantity it could be cheaper...they also quoted for cutting - 50p/cut as a rough ballpark but cheaper on multiples.

I'll get a bit further with the design & then start a build thread - then you can start ripping my plans apart again ;-)

[JAZZCNC]

I'll get a bit further with the design & then start a build thread - then you can start ripping my plans apart again ;-)

We don't Rip apart we give Con-crushing Criticism.!! . . . Opp's mean constructive Criticism.

So 4.10mtr = £30.75 for 7.5mtr, so that's same price has just 2mtr of Alu Profile or put another way you get 5.5mtr free for same money. . . . . Bit more pleasant on the Old wallet isn't it.!!

Crack on and let the fun begin.