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CNCBlug
16-09-2010, 12:16 PM
Since I am going to spend some dosh building a good 1600 x 1000 bed for my dream wood cutting machine, I was wondering if it is feasable to look at having one bed for milling and plasma cutting.

*Design is a gantry type with Dewalt router.

One day when I am all grown up I might have more space and I can have 2 machines stading around. I will also have enough money then to pay for another bed ;)

Anyway, what are your thoughts?

Also, since I know just about zip about plasma cutting, and it seems "very useful for everything but I cant think of anything right at this moment", can anyone suggest a cutter/welder model out there that can be used on above said bed?
That is to cut up to 10mm steel/brass etc.

routercnc
16-09-2010, 01:56 PM
I think there are different and opposing requirements for a miller/router vs plasma machine.

Milling gantry is strong,stiff and heavy, and plasma gantry is light and nimble. This is driven by the tool forces which are high for the miller and virtually zero for the plasma. This makes the combo you suggest a bit of a compromise between the 2.

CNCBlug
16-09-2010, 02:13 PM
The miller is the primary focus and will be built with no compromise in terms of speed/strenght/rigidness.
If you then *have* the milling gantry, why not just use it even if it is overkill compared to what you need?
Is it not just a case of getting the cutting head around at the right speed?

Take florins' design for instance (http://www.mycncuk.com/forums/showthread.php/1984-My-new-4-axes-wood-processing-CNC-router...?p=13298&viewfull=1#post13298) Why cant you use a cutter on this design?
Of course I know that you are going to burn the bed away, thats obvious, so you will have to swap it out if you are cutting metal.

BTW: love your machine florins

Jonathan
16-09-2010, 03:26 PM
I'm thinking of doing something like this on my machine which is built for milling (see my build log) so it's quite heavy to say the least. I've not looked into plasma cutting much but I think routercnc is saying that you might not be able to get the router/mill to move fast enough for plasma cutting, since the gantry is so heavy?

Just had a quick look at feedrates and it looks like upto 3800mm/min could be required, but again I'm not sure...That should be achievable on a router with good motors etc, but maybe acceleration is going to be an issue?

The bed on my router is 18mm MDF, so not best suited for plasma cutting! However I've made the travel on the Z axis 400mm, which means I've got plenty of room to fix another bed say 350mm above the MDF one on a steel frame. I think this could be your best bet. Making it so you can raise the Y axis is also an option.

It's also just occured to me that 400mm is enough to bolt my big wood lathe to the router! So I could use it as a CNC mill/router/plasma cutter/lathe!

CNCBlug
16-09-2010, 03:51 PM
Thx Jonathan

I was hoping to achieve 4500mm/min at least on my build, and with the router taken off the gantry it will help with the acceleration. If I could only achieve something like this http://www.youtube.com/watch?v=6m0j7SYkZSg&feature=related it would be more than enough for the bits I would like to do.

coxy8329
17-09-2010, 10:20 AM
Why not use 2 gantries? one bed, a heavy stiff gantry for milling and another light nimble gantry for cuttling.

Jonathan
17-09-2010, 12:55 PM
Why not use 2 gantries? one bed, a heavy stiff gantry for milling and another light nimble gantry for cuttling.

That could get expensive since surely you would need 2 sets of rails for the Y and Z axis', and 2 more ballscrews...

It would make an interesting machine to have 2 gantries running at the same time!

FatFreddie
17-09-2010, 01:32 PM
That could get expensive since surely you would need 2 sets of rails for the Y and Z axis', and 2 more ballscrews...

It would make an interesting machine to have 2 gantries running at the same time!

You could share the X axis rails and ballscrew - you'd just need to bolt the ballnut to the gantry you wanted to use. The plasma gantry would be relatively cheap to build as it doesn't need a powerful motor or high stiffness linear bearings.

One consideration would be choosing an X axis stepper that had the torque for routing and the speed for the plasma but you could always gear it and swap the sprockets over.

Jonathan
17-09-2010, 01:42 PM
You could share the X axis rails and ballscrew - you'd just need to bolt the ballnut to the gantry you wanted to use. The plasma gantry would be relatively cheap to build as it doesn't need a powerful motor or high stiffness linear bearings.

Yes I wasn't suggesting that two sets of screws/rails would be needed for the X axis. Good point about not needing high stiffness bearings...what about these:

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4485499

They're rated for high speeds, and cheap...



One consideration would be choosing an X axis stepper that had the torque for routing and the speed for the plasma but you could always gear it and swap the sprockets over.

Yes I think having a pulley/timing belt on the X axis is a must. Thinking about it if you had pulleys on all the axis then perhaps one could get the machine fast enough with the milling gantry since it could, with a bit of experimentation, be geared for much higher speeds since you no longer care about cutting force.