Gathering ideas for a new CNC router-mill thingy

I was looking at buying one of the 6040/3040 import routers but after reading many threads on them I think I can build a better unit myself. I have built two CNC plasma tables to-date, both successful and my last 1250x1250 is my main production machine now.

I went against the odds when designing it - everyone was leaning towards very large rigid gantries and heavy frames etc. I decided to use thinner 2mm box section throughout and gain rigidity only where needed by correct use of bracing and ribs etc.

The result was a 100% success and was even FEA tested with flying colours:cocksure: proof of the pudding is in the eating and it worked very well.

Now, after reading dozens of threads on building a mini router/mill for engraving and light work in alloys or wood etc, I saw a trend towards heavy builds again, some very heavy! Considering the average mill cutter is about 3mm for alloy work, maybe a little larger, and engraving tools are tiny I thought of applying my ideas to building one.

My want is for a general purpose machine - wood, alloy, plastic, engraving, carving, milling, envelope maybe 400mm x 500mm.

So, picture if you will, no box-section, use maybe 15mm x 150mm aluminium to make a shoe-box structure - 4 sides and a base (base can be thinner i think).

Mount 15mm HiWin rails to the tops of the long sides, 2 carriages on each side. Mount 1610 ballscrew on outer side of longer sides.

Make gantry base to span the opening, deep enough to take two carriages suitably far apart, drop plates down from ends to fix ballscrew nuts to - it would be an inverted U shape.

Build gantry as required from base up to hold Y axis and Z axis.

May even consider using steel plate throughout.


What do you all feel about that?

IMHO, i can't see enough counter-force coming from the small tools used in these machines to distort a 500mm x 150mm slab of aluminium by any amount that matters??

I have other ideas but this is the most radical so i thought i'd plant that one first :cupcake:

Even with smaller cutters if you want decent speeds and doc you will need rigidity. The heavy builds are to deal with vibration and resonance that the tool generates as it cuts.

Ok, i have the basic design sorted with the generous help of a forum member.

I have a nice lump of ground cast iron 18mm thick for a bed, what is the preferred method of fixturing - a matrix of holes or built-up T-slots??

This will be a multipurpose machine metal through to wood being used.

Any preferences???

Too much metal on the Z axis?

I have ordered a bit too much metal and linear rails for the front plate of my Z axis, the back plate is 320 tall but for some reason i ordered 400mm plate and rails for the front plate where the spindle mounts.

Should i leave the extra or cut it down to match the back?.

Is it generally a good thing to have maximum space between the linear carriages on the Z axis?
I had originally sketched around 30mm but after drawing it up fully it lookalike i can go to about 70-80mm apart.

It might be a good idea to post up your sketches so that they can be commented on:confusion:

Backplate attached, not shown but its 160mm wide, 20mm thick aluminium machined tooling plate, same for the front plate.

Attachment 17602

Blocks are HiWin HGH20CA narrow, screw is 1605.

If i use full 400mm front plate i can space blocks much wider which i think is generally a good thing?

Attachment 17603

If we bring in the plates that are fixed to the rear side which connect the X axis carriages to the gantry rails, it works out very nicely i think - the plates are directly connected to the z axis carriage positions.
Attachment 17604
Plates are dimensioned as 15mm. bottom two are the gantry lower/upper sides and top one holds the z motor

Metal arrived today, will be on the mill this weekend i think :)

Ballscrews - with a stepper drive system and 1610 screws, is it allowable to let the nut hit the BK/BF blocks as a means of hard-stops or do i need to also fit physical stops before they hit?

The machine will have full limit switches so will not be ploughing into the ends too often hopefully ;)

Quote:

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Originally Posted by Davek0974

If we bring in the plates that are fixed to the rear side which connect the X axis carriages to the gantry rails, it works out very nicely i think - the plates are directly connected to the z axis carriage positions.
Attachment 17604
Plates are dimensioned as 15mm. bottom two are the gantry lower/upper sides and top one holds the z motor

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Dave Think you have been got by Classic Gotcha.?
How are you going to access the holes for fastening the rear plate to the bottom bearing plate.? The Z bearings fasten from back side so can't fit when rear plate is fastened. You'll need to Lift the bearings so can access the bolts.

Quote:

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Originally Posted by JAZZCNC

Dave Think you have been got by Classic Gotcha.?
How are you going to access the holes for fastening the rear plate to the bottom bearing plate.? The Z bearings fasten from back side so can't fit when rear plate is fastened. You'll need to Lift the bearings so can access the bolts.

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....Scurries off to grab the drawings............

Ok, it definitely seems to work for me :courage:

Attachment 17634Attachment 17635

Assembly would be to screw the x axis support plates on at the bottom and middle positions, then there is just enough clearance to pass the screws from the back to the front to mount the Z axis carriages, bottom line is tight but room should be ok.

:courage:

Build log started here...

http://www.mycncuk.com/threads/9577-...7182#post77182

Ballscrews

Never used these before, the motion stuff arrived today :)

Questions...

Is it normal for the BK/BF end support bearings to be a press-fit? (Don't want to go forcing and break something.)

Do the nuts have to remain fitted or can they be removed without losing all the balls??

Quote:

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Originally Posted by Davek0974

Questions...

Is it normal for the BK/BF end support bearings to be a press-fit? (Don't want to go forcing and break something.)

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Do you mean they are Stiff to get on screws.? Or the bearings are pressed into the BK block.? If just stiff to get on screws then yes this can happen, just give the screw light rub with emery and they'll go on.

Quote:

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Originally Posted by Davek0974

Do the nuts have to remain fitted or can they be removed without losing all the balls??

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DONT REMOVE the balls WILL fall out. If you want to remove the Nut then you need tube the same size as the minor diameter of the screw and then rotate the nut onto it.

ok thanks, will leave nuts on screws.

I was surprised how big/heavy the spindle is :)

Ballscrew alignment...

How good does it need to be?

Obviously the simple answer is "perfect" but, how many here can honestly say their ballscrew / nut / motion system is perfectly aligned??

So, what sort of tolerance is there, clearly if its way out then the nuts will bind, motion will lose steps and things will fail quickly but if only a little off of perfect?

When assembling my new build i have the rails on one side of a 45x90 beam and the screws on the other side, I aligned the rails and BK/BF blocks carefully with a vernier to the same reference surface of the beam to within 0.05mm.

However, there is naturally some discrepancy when it comes to tightening the nut mounting blocks down to the travel system, I have used some shims to get shaft deflection as close as possible to zero when tightening them down.

Or is it better to float the BK/BF blocks and then clamp the nuts, wind the travel to each end and tighten the BK/BF's up then??