Cast aluminium gantry router

Hi all,
I'm starting a build thread for my machine and I'll see what you all think of it. I run a small aluminium foundry and a cnc router is something that'll be useful for making patterns for me.
I'm going to be casting a lot of the parts for it and I haven't seen another one like this on here so I hope you'll enjoy.
I've bought the rail, ballscrews and a 2.2kw spindle and VFD, here's the shopping list so far.

SBR20-300/600/1000mm linear slide guide shaft (6 fully-supported rails+12 SBR20UU bearing blocks)
Anti backlash RM1605-350/650/1050/1050mm-C7(4ballscrews+4ballnuts+4endmachinings)
4 sets BK/BF12 bearing end supports with locknuts and circlips
4 pcs 6.35mm*10mm(motor*RM1605) couplers

I've started the pattern to cast the gantry and I'll post pics as soon as I can find the cable for my camera.

I am very intrested in this build, I have often thought about using cast parts for gantry ends and such. Looking forward to seeing the pics and best of luck with the build.

Sounds a very interesting build I so will be watching to see how it goes. I do like the idea of casting some parts.

Once you have successfully cast your parts, do you intend to offer cast parts for sale on the forum? If you do I am sure that you will soon get some customers for gantry ends, motor mounts etc. Good luck. G.

Looking forward to this....always fancied making cast Ali parts...

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Originally Posted by GEOFFREY

Once you have successfully cast your parts, do you intend to offer cast parts for sale on the forum? If you do I am sure that you will soon get some customers for gantry ends, motor mounts etc. Good luck. G.

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I agree, I think specialised cast parts would make for a good kickstarter. I would buy a nice cast gantry end that incorporated machined mounting points for linear bearing blocks and ballscrew mounts

Good idea about the kickstarter, maybe I should keep all my ideas secret in case anyone nicks them :)
Sod it, here's some pics.
Here's the start for the gantry pattern. It's 19mm thick and longer than I need as I'm thinking about doing a kit and the gantry can be cut to size. All needs to be sanded smooth and all the inside corners need to have wax fillets put in.

Attachment 12539Attachment 12538Attachment 12537

Out of interest, is it expensive to get a mold cast if I supply a pattern. Just curious as I have some product ideas?

Good idea and i am interested about the process.
One thing that you should have in mind ( i have read it once in a Greek forum CNC HOBBY - CNC Mills, CNC Lathes, CNC Routers, Metal Casting, Servos, Steppers, Motion Control ) is that after Casting the aluminum shrinks according to a shrinking Factor. That Factor i think isnt stable as shrinking may be affected from humidity, temperature.... So that means that you cannot make by casting parts that have acurate dimensions near 0.1mm. Of course you can make your parts and then mill them to the dimensions that you want.

Good luck and keep trying

No casting is good enough to use straight out the mould they all need machine prep work to be used and this is where the time and money comes into affect to make accurate surfaces etc.!!

Would make a good Kit for someone with access to milling machine but for a Kickstarter and to be useful straight out the box I don't think they'd be cheap enough to produce and be attractive.?

I don't see why you would want to cast a gantry. The open back structure significantly limits stiffness.

If you compare it to a simple 80x160x4mm steel RHS section you would need to make the cast aluminum 'C' shape gantry have web and flanges of 60mm thick to match the bending and torsional stiffness.

Makes much more sense to cast the end connection down to the bearings blocks and ballscrew, with a neat interface to say a 160x80 RHS steel gantry.

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Originally Posted by routercnc

I don't see why you would want to cast a gantry. The open back structure significantly limits stiffness.

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But we're not limited to just one beam, so you could get the torsional stiffness by casting two beams in one piece. I'd go for something similar to the gantry design on my last machine:

Attachment 12545

The Y-axis rails may have to be moved and it would take a fairly big milling machine to mill the rail mounting surfaces.

Still haven't finished the gantry pattern as I'm flat out with work but I'm doing bits in between jobs.
I do know about shrinkage in casting, rule of thumb is 1/4" per foot,my alloy is 1-1.3%. It's accounted for in the pattern.
For anyone asking why? Here's why, I just want to cast it to see if it can be done and work.

The price of doing it in aluminium plate is crazy compared to casting it and once a pattern is made for casting you can repeat over and over. It'll all be one piece so no marking out, cutting and bolting plate together.
I can cut this to length, machine the ends then top and bottom for the rails and wherever parts are to be mounted. I might even bolt 2 castings back to back and make an "I" beam from them.

Watching with interest. G.

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Originally Posted by jrcast

I can cut this to length, machine the ends then top and bottom for the rails and wherever parts are to be mounted. I might even bolt 2 castings back to back and make an "I" beam from them.

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Don't bother with the I-beam idea - rubbish torsional stiffness.

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Originally Posted by Jonathan

Don't bother with the I-beam idea - rubbish torsional stiffness.

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True, but to pick up on your initial idea of twin beam arrangements you could arrange them like this:

[] instead of ][

[] has similar vertical stiffness to ][, slightly better fore/aft stiffness, and massively better torsional stiffness. If you cast it then you can include baffle plates at intervals so long as you also bolt through these as well.

A simpler alternative is to do |] where ] is the cast part (with optional internal baffles or ribs) and | is a simple closer plate.

Still lots of effort all round but they are possible configurations and much better than just ].

Quote:

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Originally Posted by jrcast

Hi all,
I'm starting a build thread for my machine and I'll see what you all think of it. I run a small aluminium foundry and a cnc router is something that'll be useful for making patterns for me.
I'm going to be casting a lot of the parts for it and I haven't seen another one like this on here so I hope you'll enjoy.
I've bought the rail, ballscrews and a 2.2kw spindle and VFD, here's the shopping list so far.

SBR20-300/600/1000mm linear slide guide shaft (6 fully-supported rails+12 SBR20UU bearing blocks)
Anti backlash RM1605-350/650/1050/1050mm-C7(4ballscrews+4ballnuts+4endmachinings)
4 sets BK/BF12 bearing end supports with locknuts and circlips
4 pcs 6.35mm*10mm(motor*RM1605) couplers

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I got exactly the same kit for sale !!! you would of saved a few pounds lol
Casting alloy parts would work well, i was looking at casting my z axis assembly until i realized it would need machining to to get the finished parts !!
I cant wait to see this build take shape it will be pioneering at its best !!