Fixed gantry table options

[v2tiller]

Hey everyone. Im at the point with my build that its time to look at table options. In Australia there isn't much available. I've seen some nice 20mm thick steel t slot tables from world of clamping in the states but the prices and shipping kills it.
So i have 2 options im looking at both similar prices.
450 x 450 19mm thick cast aluminum tooling plate or 20mm thick mild steel plate.
They will be drilled and tapped in a grid pattern.
The ally will be hard anodised.
The steel will be ground both sides and hardened after holes are added.
So the ally will be lighter but will it as durable steel? It will have vices being bolted to it and im sure ill be dropping material, tools etc on it from time to time.
I see most people seem to use ally but im leaning towards steel?

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[peteeng]

Hi V2 - When you say hard anodised do you actually mean hard anodised? Not many places in Oz do that. But normal architectural anodising is fine but spec 20um thickness. Clearly the aluminium will not be as durable as hardened steel but then it will be lighter. So depends on what speeds and accels you want and what motors you have to achieve them. Have you tried D&D Barry for the tool plates (alloy and cast iron)? not sure about price...Cheers Peter

[v2tiller]

Hi pete. Wasn't sure about the hard anodizing. So many things we miss out on here in aus. I've seen D&D Barry online. Might check them out for a quote. I've got a quote for the ally from Calm aluminum and the steel plate from a guy who does blanchard grinding up here. He will supply and grind.
My machine is running 425oz nema 23's, 10mm pitch leadscrew.
I only have 450mm travel so speed isnt too critical.
Been also looking for any old cast t slot milling or welding tables but the ones that rarely come up are usually over a grand. Too much for my budget.
Definitely leaning towards a steel table.

[wizard]

Often the cast iron T-slot tables and pallets you see in the USA cheap are imports from China so you might want to look for suppliers in China to import from. Note that pallets from old CNC work cells can often be retasked as tables for small CNC routers. It is a matter of finding a supplier of used machinery or having access to a junk yard / recycle center that captures these old pallets from the waste stream.

Honestly I wouldn’t use steel in this application if I had Aluminum, steel and cast iron available to me equally. The problem with steel plate, especially cold rolled in the built in stress that can make achieving flat and parallel surfaces a chore. You might get lucky with hot rolled plate but at the same time you should allocate extra funds for reprocessing. The guy doing the grinding for you should have given suggestions for plate steel he has had good luck with. There are options like stress relieving ir normalizing but they just add costs.

This is where used cast iron tooling plates / CNC plates, have an advantage in that they have likely relieved themselves and are not likely to distort wildly if machined (resurfaced). Even new plates will be better that the crap shoot that steel can be

So I’d stay away from steel due to it being a bit open ended cost wise. Aluminum will be fine anodized or not. Here is the thing anodized aluminum, cast iron and even steel will dent if hit by something hard or heavy. That is one reason why a machinist takes care when mounting a vise or fixture. Plate steel, aluminum or cast iron is pretty soft compare to the things that might get dropped on them. Hard answer riser aluminum of course has that hard surface but that really will not prevent dents.

Before you go the aluminum route though I’d talk with the local anodizing providers you have for an alloy recommendation. Look for an alloy /temper that is better than pure aluminum at providing a good core. That is an alloy that is tougher than dead soft aluminum but yet take anodizing well. The other thing here is thread holding, aluminum as you know strips out real fast. The right grade of aluminum with a proper anodizing though has surprised me with the ability to hold threads over time. You need to consider how you will do thread inserts and the additional costs there.

So for me it is a toss up between Aluminum plate and cast iron tables / pallets. Well that and your expectations. I’d probably would want a thicker aluminum plate but that is me.

[Goemon]

The first question should be, what will you be milling on this machine? large cnc mills use cast iron because of it's superior vibration damping (vs steel or aluminum). Controlling vibration is key when milling hard steel with large end mills.

If you will only be doing light hobby woodwork, you might be better off using aluminum (for a diy project). Those industrial cast iron and steel T-slot milling tables weigh a ton. This is why they use large Nema 34 motors (or ac servos) instead of small nema 23 steppers in those Bridgeport cnc conversion kits.

Surface hardness is not massively important for the table. Stiffness is what matters. Tool steel is hardened for tool and knife edges so they can remain sharp for longer. The hardening does nothing to increase the steels strength or stiffness. It does the opposite and makes it impossible to work on later. Anodizing aluminum is a similar waste of time.

Aluminum is relatively light and easy to work with in a diy setting. A tempered alloy (t6 or t7) will hold screw threads just fine. With a little patience, you could probably face it and cut the t-slots yourself on the cnc machine you are building. A t-slot plate is the first thing I made on mine.

There are other options too. My (moving) table is a vere vibration isolation table. It has a steel shell with some kind of honeycomb center and it has an aluminum optical breadboard on top (which is what I mounted my t-slot plate to. These come up used on ebay regularly and a smaller one might be light enough to ship to Oz.

[ger21]

The first question should be, what will you be milling on this machine?

+1

If you're just cutting wood, a couple layers of plywood and/or MDF might be sufficient.

[v2tiller]

Thanks for the replys.
I'll be using this machine to cut plastics and aluminum mainly. Sheet on the table and blocks in a vice.
Unfortunately where i am used machinery goes to scrap pretty quickly so its all luck of the draw if you can find anything.
I will have have a chat to the guy who does the steel grinding. He has 40yrs experience in the industry.some of the pics of 40mm and 80mm plate he has processed look amazing.
In the end this is starting as a hobby with hopefully doing a few small jobs here and there. Im already hooked on cnc as most here are and down the road would like to get a small/med vmc in the shed.
Im going to mock up a mdf table just to get going.

[v2tiller]

Found a place that sells precision cast iron and ally plates. Going to get some prices.
The sizes are a bit smaller but i can live with that.
I can get a 315 x 400 cast iron plate in either 25mm or 36mm. 36 is getting a bit too thick for me, losing gantry height.
But will 25mm be strong enough in cast iron? There are no ribs or anything just flat plate.