80/20 aluminum gantry, milled aluminum ends

[3Dsigns]

This is something I've wanted to do for a long time. Its the gantry I'm working on for a homebuilt router. The main extrusion is 3"x6" 80/20 aluminum, 60" long.

Questions

The milled piece on the end came from another CNC machine in a textile factory and is 3/4" thick aluminum alloy. Will it be strong enough to carry this gantry? If you can see it in the photo, it also has another piece of 1/4" plate mounted to the back, also attaching it to the 80/20 beam, so that should brace it very well laterally. The gantry will probably weigh close to 100 lbs with the stage, racks and motors installed and it's already heavy with the linear rails installed.

The thing that concerns me, is that the end is milled to hold only one bearing block. Is this enough? Or do I need two? Because I plan to use rack and pinions with servo motors ,instead of steppers, to drive it. Could the acceleration of this setup create too much G forces along the x axis, for one bearing block to handle?.

Thanks!

[Benonymous]

I think we need a couple of detail pictures. It looks fairly well thought out as a structural part and one bearing block with a R&P setup should be OK. What is the material thickness? It looks 10 to 12mm to me which should provide adequate rigidity.

[3Dsigns]

Thanks,
It's made of 3/4" plate
The "brace" behind it is 1/4" thick and bolts to the T-slots in the gantry beam and se3veral places along the back of the end. Once everything is lined up properly, I suppose I could weld it too. But you think one block is OK?

One other question; since I only have one of these ends, how hard would it be to get another one milled for the left side? I have a ShopBot. If I cut in several passes, could the Bot do it?

[Benonymous]

Ahh, you only have one of these...

This is where you get into the situation I'm in. If you design your machine around scrounged/repurposed parts, you get locked in to some decisions that, without that scrounged part, you might make differently. Ask me how I know!

I'd seriously think about just using this part as a pattern and if you're prepared to make a new part to match this, why not go all the way and make a gantry end that can take two blocks? While you're at it, make two...

Anyway, just a suggestion.

[3Dsigns]

Originally Posted by Benonymous Ahh, you only have one of these... This is where you get into the situation I'm in. If you design your machine around scrounged/repurposed parts, you get locked in to some decisions that, without that scrounged part, you might make differently. Ask me how I know! I'd seriously think about just using this part as a pattern and if you're prepared to make a new part to match this, why not go all the way and make a gantry end that can take two blocks? While you're at it, make two... Anyway, just a suggestion.

Thanks!
I can duplicate the pattern pretty easy, and add to it for another bearing block, save it as an EPS file and make toolpaths in My CAM program.
Is an old ShopBot capable of milling the parts in this thickness of material? If I cut in several passes?

[Benonymous]

Sorry, I have no experience with the ShopBot. If it's a light weight/duty machine, yes do the part in nice easy passes :-)

[CarveOne]

Originally Posted by Benonymous Sorry, I have no experience with the ShopBot. If it's a light weight/duty machine, yes do the part in nice easy passes :-)

Most of the Shopbot models can handle aluminum without serious problems. They are very popular in the US.

CarveOne

[3Dsigns]

Thanks guys!

[3Dsigns]

Oh yeah
I've never machined anything like this before....would a spiral endmill be best?

[CarveOne]

Originally Posted by 3Dsigns Oh yeah I've never machined anything like this before....would a spiral endmill be best?

Use a standard center cutting 1/4" end mill made for cutting aluminum, keep the rpm as low as you can reasonably get it, and spray a shot of WD40 on it occasionally to keep the aluminum from sticking to the cutter. It will gall if the rpm is too high. Practice on some scrap aluminum of the same type before committing to a 'real part' cutting session.

CarveOne

[jsheerin]

I would use two bearing blocks personally. My router uses the 3060 extrusion as well, and I have two bearing blocks that span about a 1 foot length. It seems to work okay, but I am using steppers and acme screws which keeps accelerations pretty low. If you're using servos I'd definitely want two blocks. Pics of my setup here:
Index of /HORNS/images/cnc

You could cut aluminum with a typical router. I used mine to cut a 1/2" thick (iirc) piece of mic-6 tooling plate for mounting a Kurt-style vise on - worked great. I used a really small depth of cut - like 0.020" per pass, but I try to turn the feed rate up as high as sounds good and the spindle speed down as far as possible (about 10k rpm for me). If you have more power or your machine is stiffer you might be able to get away with more. I never had to use wd40 (or other lube) while cutting larger slots, but if I didn't use it when pocketing smaller holes the aluminum would quickly weld to my cutter, jamming it and breaking it quickly.

[3Dsigns]

Thanks!