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Rainbows
06-07-2017, 05:30 PM
Been making up a shopping list for a moving gantry I want to make.
Aim is 640x440x125 work envelope to machine wood and aluminium. Mild steel would be nice too but I'm not sure what standard of build is needed for that and I'm not about to make anything extreme in weight or budget.

My first hang up is not being sure on what size rails for the Z axis. X and Y are to use 2 HGR20 rails each with 2 blocks on each rail. For the Z axis I didn't know if I could skimp out a bit and use MGN15 or use only 1 block on each rail.

Much of the frame is 100x100x5 box section that I have hanging about. Going to have it surface ground before installing the rails

EddyCurrent
06-07-2017, 11:37 PM
Why would you want to go cheap on the Z axis ? it's one of the most important parts.

I used 15mm rail and blocks for Y and Z but never again. They work fine but unless they have changed the design, getting grease into them is damn near imposssible.
See this thread; http://www.mycncuk.com/threads/7273-Greasing-Hiwin-HG15

This was my solution if it's any use to you.

I got some 4mm tube, push fittings that I turned down to fit in the gap, and there was just enough 'meat' on the push fittings to reduce the 5mm thread as supplied down to a 4mm thread that fits the Hiwin bearings.

Fitted some brackets with 6mm thread push fittings, 6mm thread nipples, and 6mm hex connectors.
It now works very well.

I also fitted a home made extended brass grease pipe for the Z ball nut grease nipple.

Pic1 shows it with Z front plate removed, pic2 shows it reassembled.

22110
22111

Nr1madman
07-07-2017, 03:16 PM
Nice Mr Current!! What kind of grease are you using for those bearings?

EddyCurrent
07-07-2017, 04:30 PM
Some of the links I used a while back are now dead but at the time I found some cross reference charts and worked out that for light duty use Lithiun EP1 and heavy duty use Lithium EP2
this is the one I use ; http://www.toolstation.com/shop/Automotive/Mechanics%20Tools/Lithium%20Grease/d60/sd180/p89691

Read this; http://www.intercom.si/web/dokumenti/HIWIN_LI_EN_V1_1.pdf

Lee Roberts
07-07-2017, 06:26 PM
Nice little manifold would be easy to nock up:

22113

You can buy them in various flavors as well: 1/4" PT Threaded Ports 3 Way Quick Connect Air Hose Manifold Block Splitter (http://www.ebay.co.uk/itm/1-4-PT-Threaded-Ports-3-Way-Quick-Connect-Air-Hose-Manifold-Block-Splitter-/182286105001?epid=1749478979&hash=item2a711939a9:g:tzYAAOSwmfhX3z0K)

Or another member did his with one of these push fits: Pneumatic One Quick Push to Connect Union Manifold Connecter 5 Way OD 8mm (http://www.ebay.co.uk/itm/Pneumatic-One-Quick-Push-to-Connect-Union-Manifold-Connecter-5-Way-OD-8mm-/221070133903?hash=item3378ce8a8f:g:nr8AAOSw7PBTopZ X)

routercnc
07-07-2017, 07:07 PM
My current machine uses 15mm rails on Z and cannot recommend it. Lots of reason including stiffness , packaging ball screw
Go 20mm

If you want to do steel convert a mill else you really need to go to town on a router

Rainbows
08-07-2017, 03:08 PM
The beginer moving gantry pinned thread mentioned that you if desperate could skimp out if desperate on unsupported rail for the Z axis, now realise though thats probably because it has a short span compared to the other axis rather than it being under low load.

Clive S
08-07-2017, 04:55 PM
The beginer moving gantry pinned thread mentioned that you if desperate could skimp out if desperate on unsupported rail for the Z axis, now realise though thats probably because it has a short span compared to the other axis rather than it being under low load.

The Z axis gets the most load although 15mm rails will do the job there are good reasons to use 20mm and they are not much different in price. You will find it difficult to get the ball nut in using 15mm as you have read most people that have used 15mm say they would not do so again.

EddyCurrent
08-07-2017, 07:05 PM
Also if you did use unsupported rails of substantial proportions then the moving Z plate might end up some distance from Z back plate thus creating a cantilever and increased turning moments.