[temo57]

Hello

Si i've been drawing on a mill design for a hobby prosjekt, my goel have been to come up with a bolt together design with the Y and Z axis in one part, to avoid the flex and alignment issues with a Z-axis that bolt on the base of the Y-axis.

I've used 30 mm steel plates with a base height, depth and width of hense 800x750x300 mm, as shown it will weigh inn at about 400 kg.

I guess it will be too expensive to build with the steel prices for the moment, but my question is: what accuracy can one expect on a build like this with precision milled parts just bolted together with bolts and loctite?
I guess it will be too big to precision grind the base of the rails for the Y and Z axis after it's assembled?

Terje

[ardenum]

Precision grinding surfaces sure is a hassle and major expense. For a hobby machine, it probably isn't needed. I switched to build on top of precision granite slabs because I can lap the surfaces as needed even down to 1-2um. Bolts+loctite some may argue is almost as good as welding.

[temo57]

Thank you.
No, that’s my big question, do I really need the tightest tolerance for my build. I was thinking of using a well renomed workshop to do the milling of the part’s and assembly the part’s on a “perfectly” flat welding table in a jig. https://www.siegmund.com/en?i_am_from=en&cookie-approved=1&google-enabled=1&youtube-enabled=1&gdpr-close=1
So do you mean that you assemble on a precision granite slabs or do you actually use them to build with, if so do you have some examples?
I guess that a precision granite slabs of some size would be very expensive, what grade of slab are you using?

[peteeng]

Hi Temo - Comes down to how "precise" you want the machined parts to be that you want to make. The bolted together philosophy is valid. You have to select motion parts and processes that achieve your required machine accuracy. 0.1mm ? 0.01mm or 0.001mm? all doable just comes down to $$$. Peter

You have a Kress on a thin mount, this will vibrate. You need to have a spindle that matches the machine stiffness to get the most out of the machine. Or you back off the rest of the machine to match the Kress. The Kress is more of a router spindle then a mill. There are a few aluminium plate machines like you have designed in the forum. Perhaps look at those, working in aluminium sometimes has advantages vs steel. This sort of design depends on accurate, square and parallel edges. Easy to do in CAD not so easy in reality but if you have a workshop with correct machines for the job very doable....

[ardenum]

Thank you.
No, that’s my big question, do I really need the tightest tolerance for my build. I was thinking of using a well renomed workshop to do the milling of the part’s and assembly the part’s on a “perfectly” flat welding table in a jig. https://www.siegmund.com/en?i_am_fro...1&gdpr-close=1
So do you mean that you assemble on a precision granite slabs or do you actually use them to build with, if so do you have some examples?
I guess that a precision granite slabs of some size would be very expensive, what grade of slab are you using?

I'll use them to build the thing. Although it is not a VMC(vertical) type of build like what you conceptualized. I made 3 concepts with granite slabs so far, a router build like datron M8, a double column raising gantry like DMU 210/270P and a moving column like DMF 200/8. As of now I'm leaning towards a moving column but with an HMC config(horizontal).

Granite slabs can be expensive, for this build I'll be using grade 00 from https://www.messmaschinen.org/p/mess...0-120-guete-00.

For examples you can check my thread: https://www.cnczone.com/forums/cnc-d...-concepts.html
I haven't posted the granite versions yet, but the moving column is basically almost identical to its granite twin.

As Peter mentioned the spindle is a big part of the stiffness equation, take a look at something like this https://de.aliexpress.com/item/1005001955171225.html. Y

How expensive is Siegmund GmbH? Initially I was also planning to send of my machine to a machine shop but the quotes I got were horrendous. Sometimes even more expensive than the whole machine.

[temo57]

Yes I know, the Kress is really just for illustration purpose. I've been thinking of using some 15 mm tool plates mic 6, they should be fairly flat, what do you think?
I will mainly be doing prototype work on my own prototypes, so I can set my own speck for accuracy, haha.

The granite approach seems interesting, do they do custom sizes with all for sides at grade 00, so you get them precut, what about inserts?
Here in Norway prices for steel, aluminium and I guess granite to is just ridiculous for the moment, not to talk about machining.
The tables start around 2.000 usd and upwards, up to nearly as much as you like. I've seen they drop a car on them. https://www.siegmund.com/nb/Videoer-og-filmer,6304.php

[peteeng]

Hi Temo - If your open to granite then cast your parts in UHPC or CSA grout with steel/aluminium inserts then have it machined. The grout is much cheaper then metal... There's a few epoxy granite / concrete / polymer concrete / etc threads in here. Peter

[ardenum]

The granite approach seems interesting, do they do custom sizes with all for sides at grade 00, so you get them precut, what about inserts?

They can do any shapes and sizes and also do inserts but that can easily get into the same price range as if you cast your parts in UHPC and had them machined at a company. The standardized slabs they sell have grade 00 only on the top surface and are therefore on the cheaper side. You'd have to send them a .step of the part with inserts and ask for a quote to know for sure.