DIY 400mm CNC mill

[richb77]

http://s281.photobucket.com/albums/kk208/HOG1450/?action=view&current=cncmill.jpgI've been working on my chassis/platform.

So far any comments? Any glaring issues (bear in mind its not complete)

I am getting confused over the ball screws ends and fixtures. Any suggestions to what goes where?

Cheers

[richb77]

OK, So Irving suggested i move my thread form a question that spawned out :)

With regards to ballscrew ends. Whats the difference between floating or fixed ends? (looking at Zappa website). I think i will go for one either end to support the ballscrew better but i am not sure the differences and wha ti would need.

Cheers

[Gary]

The drive end needs to be fixed and the other end needs to be floating.

To keep the costs down look at the pre machined ball screws unless you can machine them yourself.




OK, So Irving suggested i move my thread form a question that spawned out :)

With regards to ballscrew ends. Whats the difference between floating or fixed ends? (looking at Zappa website). I think i will go for one either end to support the ballscrew better but i am not sure the differences and wha ti would need.

Cheers

[richb77]

I have access to machinery for the next week!

What machined on them? Just down in diameter to fit what looks like a 15mm end?

[Gary]

I have access to machinery for the next week!

What machined on them? Just down in diameter to fit what looks like a 15mm end?

This is the typical machining we suggest.

http://www.slidesandballscrews.com/pdf/Machining%20600mm.pdf

This is to fit the the BK and BF mounting blocks.

[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/european/dcservo/ip57m500geareddcmotor.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/european/dcservo/ip57m500geareddcmotor.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 :(

[richb77]

The servos may still be an option now! ther eis a chance the gearboxes have survived the bin.

I am still very unsure as to what torque rting i will need to be looking at (or other specs for that matter) to get this >400mm travel aluminium machining mill working smoothly.

thanks for the help. Great knowledge base here.

[Lee Roberts]

Hows this build coming along Rich ?

[richb77]

A bit slow sadly.

I have all the rexroth extrusion ready for cutting and a bosch 500W die grinder...But an imminent house move has slowed it up a little.

I'll update ASAP i promise ;)

[Lee Roberts]

ok no problem mate !, where did you get the extrusion from ?

[richb77]

Originally RS.

I bought it whilst working for an old employer (2 companies ago!) and a mate still works there. They where having a clear out and 6 metres of it had never been used and heading to a skip!

My mate kindly swiped it for me with the corners and some other accessories.

Its hellishly expensive and counting my luck with that one.

[Lee Roberts]

Ahh thats not to bad then mate, check out KJN (http://www.aluminium-profile.co.uk/), they seem to be ok for price's. I think i'm going to use extrusion for my next machine build.

I'v just picked up a 500w Ferm router on ebay for £10, seems its just like the Trend T3 (older model to the T4), stiped it down last night gave it a clean and some lithium2 later it seems to be quite nice for the price. I cant see any movment (runout) on it, there is a few of them on ebay, the trend T's are going for £50-60 there is 1 or 2 T3's on ebay as well up for bidding and also on "buy it now" collets seem to be the problem. I'v just found a guy in USA selling a 1/8" to 1/4" collet at £12 inc p&p, seems i may have to if i want to use 3mm shank cutters :D