DIY 400mm CNC mill

[irving2008]

You may want to move the gantry along the frame a little...And brace it a tad too.

Bearings will need to be doubled and the rail needs to be of the fully supported type...Unless it's 30mm+

Ballscrews should be supported by the best method possible....

Back to work for me!

Adding to Kips thoughts (or not) I agree it needs to come more central but that depends on the overhang of the spindle. My spindle will overhang 170mm approx from the backplate so the uprights will be positioned to place the spindle at the central point of the table motion.

The table needs to be supported on 4 bearings arranged at least 65% of the table width & length apart (some simple bending stress analysis will show the best location with regard to workpice size and weight)

You may need some more bracing on the gantry sides in the X direction, depends on the size and rigidity of those green angle blocks.

I don't know what rail or table you are planning but I can tell you that a 19mm 500 x 500 sheet of MDF supported as mentioned above supported on 500mm long, 16mm dia, rails deflects .05mm in the centre under 4.5kg of load. Depending on the working load, and accuracy you require, 16 or 20mm rails may suffice - you might need a central fore-aft strut to remove a tendency for the end extrusion to rotate inwards under load (due to the twisting moment of the linear rails in their supports). The X-pattern extrusion has a high area moment of inertia in bending but is surprisingly much worse tortionally.

Looks good so far!

[richb77]

Ok, new question...

I am looking at getting my motors and dont know how to spec them.

i have been offered a couple of free mclennan M500 servo motors (without gearboxes) http://www.mclennan.co.uk/datasheets...reddcmotor.pdf

They need repair (positional optics parts) but are free

are they suitable?

what spec do i need for medium duty >400mm travel?

[Gary]

These motors are about 0.15 Nm, so will need gearing.
Also you will need to replace the encoder if it is faulty, and i would look at US digital as a cheap source for encoders.
As for if they are suitible or not that will need further investigation.

Ok, new question...

I am looking at getting my motors and dont know how to spec them.

i have been offered a couple of free mclennan M500 servo motors (without gearboxes) http://www.mclennan.co.uk/datasheets...reddcmotor.pdf

They need repair (positional optics parts) but are free

are they suitable?

what spec do i need for medium duty >400mm travel?

[richb77]

Thanks for the replies guys.

I think 0.15Nm isnt enough and they are pretty big without gearing.

Now i am thinking to repair these and gear them will be more costly than buying say 3Nm Nema 23 steppers?

Although accuracy is good i doubt very much i will need much below 0.25mm (and thats being REALLY tight for hobby use).

I may pass on the servos and just get the steppers.

Cheers again

[Smiler]

Hi Rich,

Don't wait too long mate, prices seem to be rising alarmingly.

The stepper kit I bought from Zapp only a few months ago has gone from £206 to £289!

[Gary]

Yes prices are going up, and this is due to the US dollar to the pound changing.
Only 6 months ago it was over $2 to the pound.
I just paid $5000 to my supplier in china and got $1.48 to the pound.

The rate is causing prices everywere to go up.
The drivers have just gone up, and i suspect motors to go up very soon.

I noticed prices all round increasing just lately :(