[Learning2Machin]

I currently have a converted BF20 CNC mill, and I have been toying with the idea of building a CNC machine using linear rails rather than ways for all 3 axis, and using the BF20 head, or at least the spindle.

I started out by using the base, saddle and column from the BF20, modeling everything out, removing way material to place the linear rails. I have seen some similar threads in the past. But than I started thinking, if I am going to build this thing, I probably want it to be bigger and beefier than the BF20, and would rather kind of custom build the whole thing.

My question is, could I build a new base, saddle, and column out of aluminum, or would it have to be made from cast iron or some type of steel? My thought was to use very big, beefy solid blocks of alu for everything, and just remove what is needed. I even thought about making a larger head out of alu as well, boring out the hole for the spindle.

I would still use the BF20 table, as I have no desire to rebuild one of those.

Ultimately, the main use would be for cutting aluminum, and occasionally cutting steel or cast iron. I really want speed, and I feel the ways are just such a maintenance PITA.

I suspect the biggest issues would be rigidity, as well as a lack of scraped surfaces, but the mating surfaces on the BF20 sucked anyway, and needed a lot of shimming to tram the mill in. I also know alu is lighter than iron, but the BF20 has tons of gaps in the cast iron and space, where the alu would be all solid.

Would this work? I can't imagine a whole lot of deflection. Would love to hear any thoughts on this.

[awerby]

Steel is not only stronger and heavier than aluminum, it's also cheaper. It doesn't have the vibration-dampening qualities of cast iron, but it's a lot easier to work with for most people (who don't have cupolas in their back yards). But sure; you can build a machine out of big beefy chunks of aluminum. I doubt it would cut steel or cast iron as well as a steel or cast iron machine, but it would probably work fine on aluminum. The linear profile rails wouldn't be the problem, just the lack of mass and dampening. But with the lighter weight of the aluminum, you'd be fighting inertia less, so higher speeds should be possible, especially if you fitted it with servo motors and low-pitch ballscrews. That extra speed wouldn't help much when cutting ferrous metals, but you could really fly through softer materials.

[G59]

I suspect the biggest issues would be rigidity, as well as a lack of scraped surfaces,

Well it's a little more complicated then that. The number one issue is the one, no one here talks about. Galvanic corrosion!!!
You ca slow it down but never completely eliminate it.

If you intend to used flood coolant or any type of water based coolant, the contact surfaces between steel and aluminum will corrode. Now think what it does to the underside of the rails and any other precision surface.

As awerby suggested, makeit out of steel.

[pippin88]

Consider buying a BT30 cartridge spindle. If I was scratch building a cnc machine there is no way I would use a spindle with a quill, or an R8 spindle.

[Learning2Machin]

Thanks for the feedback everyone. I tend to agree with everyone. Does anyone know if its possible to get iron castings done to your design? I would imagine it would be a fortune for one off's, but figure its worth looking into.

[G59]

Does anyone know if its possible to get iron castings done to your design?

You can and not too expensive. What cost quite a bit is the patterns, the engineering and making them oversize with proper draft and time needed to make them and the time you will spend having to cut and grind surfaces. For a one off its not needed.
Thats when it gets expensive real quick. The machining bit of it

You know steel plate with proper damping pads attached to it works very well and is cheap. Automation direct sells it I think.
Also steel is much stronger than cast Grey iron.

[CS900]

you may want to look into epoxy granite construction as well. In fact there is a whole section of this forum dedicated to epoxy granite machines. Very cool stuff!

[Uguessedit]

Could anodized aluminum.

Well it's a little more complicated then that. The number one issue is the one, no one here talks about. Galvanic corrosion!!!
You ca slow it down but never completely eliminate it.

If you intend to used flood coolant or any type of water based coolant, the contact surfaces between steel and aluminum will corrode. Now think what it does to the underside of the rails and any other precision surface.

As awerby suggested, makeit out of steel.

[peteeng]

Hi L2M - 1) Your first thought about billet machining aluminium is a good one. Except aluminium is quite live for the application. But if you had some simulation software you could figure that out so the lighter weight was to your advantage plus you would need to anodise the parts and use a sealer between assembled steel and aluminium parts. This is commonly done for al to SS in the marine industry 2) Billet steel is good too, but steel is live and dense. If you built in steel I'd have it zinc plated then painted. 3) Epoxy granite is very good so you could make simple moulds on your mill and then fill them with epoxy and alumina grit. See the last bits of this thread for advice on Epoxy Alumina castings. Personally this is the way to go for a one off build. Exceptionally damp material, can get whatever shape you want, no corrosion, material is readily available, easy to finish machine by inlaying steel or aluminium.

https://www.cnczone.com/forums/epoxy...ml#post2332016 cheers Peter