Machine bed material

Hi All
I am looking for a bit of advice on a cnc mill I plan to build. I will be getting the XYand Z beds made from either aluminum 6082 or From steel. I then plan on embedding them into epoxy granite.
Would there be any benefit with going with steel over aluminum the steel is a lot more expensive than aluminum. The X and Y travel will be 200X150 mm. Will be cutting aluminum and brass and sometimes steel. For steel I will only be cutting small parts.
The mill will be used for making some parts for watches. I have attached one of the Axis beds that will be embedded into the epoxy resin. Any advice would be welcome.

Thanks
Aust12
Attachment 30168

Why don't you type XY Table into Amazon and go for cast iron?

Forget alu.
99.9% of all tools in the world able to cut steel, are cast iron or steel.

If You wanna make watch parts, it´s not hard but a bit expensive.
Everything needs to be upsized 3x vs a wood router, and preferably 10x the mass.

Expect about 5-10k in costs for a medium diy setup.
No ??
The worlds best guys regularly spend 20k for similar.

I sold a similar industrial setup, 5 axis, for 100k€.
To one of the worlds best watchmakers, Pita, in Barcelona.
Pita is the Only Spanish member of the Swiss watchmakers horological society, about 40 members.

You *can* cut brass and alu parts with anything light, like a chinese barebones router.
But they wont be round or cylindrical or repeatable to watchmaking standards or metrological standards.
You will need to mount adjust and finish every part individually, to size, flatness, square, cylindricity, etc.
Pita used to do that.

Until I sold them the Haas OM-5 axis office mill.

And it was a knife-edge decision by Haas to approve the specs that premium watchmaking needed.
Because Haas will never ever fail, (at least Hitec Mexico and Spain) and will fix anything at any cost, they ever sold.
I know, I was part of the executive.

I personally sent the case to Oxnard, cali, and they guaranteed that the Haas OM would deliver.
They were happy with the product in Pita Barceloa.

I´m NOT saying You need to buy a HAAS mill, to do Your work.
I´m pointing out that repeatable work, watchmaking, comes out from good machinery.
Reducing manual rework.

Potentially, changing the screws (ground c0), mounts (ac bearings abec5+), linear guides (heavy preload precision class), and using industrial epoxy to fix a granite base under the bed You would get a good tool out of a basic router.
Then change the router to
1. high-speed spindle, water cooled, == 800w (you don´t need power),
2. Nakanishi NSK.

Another idea for you as you seem to require a small but very accurate machine - ever thought of starting with a "granite" surface plate? Whilst heavy, they often go quite cheap at machinery auctions.

Hi All
Thanks for the reply’s. I did think about buying a XY table but there would be a lot of machining to fit the rails and ball screws that I have.
I am only looking for reasonable accuracy for this mill. I understand that watch parts meet higher precision.
When I say watch parts I should have clarified, I plan to make some parts of the the plate, the pockets in brass the rest would be made in the watchmakers lathe. I would aso like to use it for making the some of the steel springs.
I plan to fit a 4th axis for gear cutting must of the gear work I plant to do on the schaublin 70 lathe abs the Deckel G1L pantograph. Then use the mill to cut the teeth.
I also plan to use it to make jig fixtures. I already have NSK 20mm rails and C5 ground ball screws. The cutting area will be 200 X150mm.
I am leaning towards getting the rails and plates made the rails will be 20 X 500mm and embed them into the epoxy granite. I will post a pic of what I am planning so there is a better idea of what I’m thinking.
I have a G penny 2.2kw metal cutting spindle ordered, for now that will do but I do plan to upgrade the spindle down the road.
To get the rails and plates made it’s coming in at around 1500 euro so I sappose I am looking for a bit of input on my design before I spend the money on the steel.

Attachment 30169
Pic of the structure that will be in the epoxy resins, threaded bar will also be added. The steel will be 1.7225 and with a surface roughness of .04um RA.

Bl00dy hell. 0.04um Ra?? That is superfinished, almost mirror-like. What are you going to use to achieve that?

Hi Muzzer, I won’t be doing the Machining. It will be machined in Germany. It’s going to cost a few

Quote:

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Originally Posted by Aust12

Attachment 30169
Pic of the structure that will be in the epoxy resins, threaded bar will also be added. The steel will be 1.7225 and with a surface roughness of .04um RA.

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Pointless and not required machining to this level to achieve what you want.?

Pointless because having the plates machined before embedding into the epoxy will distort them due to thermal expansion and pressure, plus the extra machine time to achieve 0.04um Ra is wasted just for fastening rails onto.! You will be paying extra for this level of finish when it's not required.

Hi JazzCNC,
Thanks for the input, I never thought about terminal expansion on the rails. The other option I was going to go was to either anchor or bolt the beds to an epoxy base I have attached an pic of the beds.
You are probable right with the .04 um Finnish, I probably don5 need to go to that level.
Attachment 30170

I'm planning to do a machine with similar design, but with concrete instead of epoxy. For the machine bed, a pre-milled plate will be layed on top of the concrete and bolts will hold it inside the concrete. I'm choosing pre-milled because I don't have any spare cnc to mill it afterwards and also not interested in scraping it. My question is what "therminal expansion" is reffered to here? Is it possible for the plate to be distorted AFTER it is layed in on top of the concrete? And i'm not asking about any distortion due to use, or environmental factors, i'm asking just about the process of laying it on top. I know concrete heats up while stiffening, but is that going to distort a 2cm thick steel plate? And if yes, i also don't care it distorts it it 1 measly micrometer or something like that. So what thermal expansion is reffered to here?

Hi all. I finally built the mill. I used 20X75mm plate aluminium for the rail bases. When I added the epoxy the rail bases shifted slightly. It worked out ok it’s accurate to 30 microns or less. I was thinking of doing a redesign to try and improve on the accuracy. I have attached the drawings of what I’m planning. It will be made out of 50mm thick c45 steel the base will measure 500X400mm. There should be a nice but if weight in it.
I know it’s preferable to make machine bases out of cast iron but would C45 hot rolled steel work for this machine. The surfaces for the rails will be ground flat. It will only be cutting brass aluminium and sometimes small bits of steel. Attachment 31896Attachment 31897

Instead of on top cast the steel within the mineral casting (Epoxy granite to some)

https://www.model-engineer.co.uk/for....asp?th=139042

There will be very little heating assuming you are using slow cure epoxy at around 15% of the mix.