Thread: DIY mill...
Yes, I did some more research... although I havent broken my airdrill out of its packaging the big issue with airpower is lack of torque and constancy of speed... so I'll go back to electric motor....
I noticed on eBay a few drill motors, 14.4 and 18v replacements for cordless.. The specs on these look promising 100W, 55Nm torque at 10mm (I need ~50W, ~15Nm) but the spindle speed will be low, maybe 1800rpm, although I read that 14v motor PWM'd at 25v will run faster... maybe I could belt drive it, 2:1 ratio will give 3600 rpm @ 25Nm...
I also came up with a plan to fix mount the motor and belt drive the spindle on a sprung idler so the spindle could traverse the Y plane but the motor remain stationary. Of course the Z motion will require a splined drive shaft so the upper drive pulley remains fixed.... I'm sure there's a catch somewhere, just don't see it yet....
I was feeling grouchy one day, reckoned my mill was overpowered at 2hp, noisy, had a poor selection of speeds and was not very quick... so I bought a pukka 1hp motor with a matching digital phase converter and computer cable.
Slow to twice normal speed with no loss of power, soft starting, reverse, da woiks.
It's been lying around ever since, but I will do it one day... honest I will
My point being that I believe the best way to drive a mill is a DPC but I have yet to explore the possibilities.
I have a feeling it would be nice if the machine could autoselect the correct speed from the G code, not start with a bang, maybe apply the brakes so I don't have to wait while it slows down etc :D
Well the design progresses slowly...
Been thinking about ways to mount my leadscrews and looking at bearings for the same, namely the 608ZZ that Lee sells...
I have some questions...
1/ Do I really need bearings for 10mm leadscrews max length 400mm. I've not done the calcs yet but gut feel says yes even if its just for the far end....
2/ whats the diameter of the inner rotating part of the race (not the shaft diameter)? My thought is to use a similarly sized OD/8mm ID washer that would act on that to preload the leadscrew with an 8mm ID thrust collar. How do others suggest preloading the screw or do you rely on the motor to control horizontal movement of the screw?
3/ Was thinking about boring out an SK12 or SK13 round rail mount to fit the OD of these races, since that would put the screw centreline at the same height as the rail centre line and is easier than constructing somehting from scratch IMHO. Do you see any issues in doing so? Else what do people suggest as a way to mount the races?
I'll have to machine the ends of the leadscrew down to 8mm (they are 10mm x 2). The leadscrew i have is 400mm long which with machining allowances will work with a 230mm table on 500mm rails giving of 460mm of travel (20mm anti-crash space!).
Not having seen how others do this close up, this is my best guess as to how to approach it. Thoughts?
To me building a cnc machine is like commiting suicide ...it just cant be done in half measures ..you either succeed or you dont. We've all tried to out think the existing technology ... you may be able to build something resembling a cnc with this drill ..but believe me ... after a week you going to be dismantling it to improve it with another idea ... this will continue for the next year .... 2000 notes and 1000 hours later ...you will be buying what you should have bought in the first place!
How do i know this --- been there --- thats is basically how we all started and hind sight can be a b****.
eBay got to me again.... picked up a brand new Dewalt D28885 500W 1.7kg die grinder as the basis for my milling spindle for £40, bit cheaper than the £100 asking price for a 500W Kress. There are a couple of places on the Net doing spares for the Dewalt and they list the spindle bearings as type/size 608VV so should be possible to upgrade them later if need be...
Still havent decided if this is going to be a fixed or moving gantry machine... I'm tending towards fixed gantry, moving table in X, moving spindle in Y & Z
I'v also got x4 SK12's sat in my office as well, but i'v just had a look and they wont be big enuff for the 608zz's. i have got lots of SK20's so you could bore them out to 22mm for the 608zz's to fit into?
This is how i went about supporting my leadscrew:
So yea i fitted a bearing at each end of the leadscrews, then i used nuts to preload? the rod a little.
I'v now made this as another solution also in the hope people will find them usefull:
This is a bearing rod support i have designed for other builders and myself, use's a small grubscrew to hold the bearing in place. A key feature of the design I believe to be an advantage over some of the mass produced supports is that it is flush fitting to your machines; this means you donít need to bore big holes to fit it.
What is the lead screw made of? There is a big difference between machining chrome moly steel and machining studding.
Best mount is one axial thrust race at either end and one powerful spring holding it in tension. This is very reassuring when you eventually chuck up your DTI, measure the backlash and have a panic attack. (Not a good idea if working in MDF though, it's about as resilient as marzipan when under load).
I was thinking that SHF20's bored out would also work as per your solution above (is that Delrin?)
I note your leadscrew runs the entire length of the axis. Although it doesnt need to - asuming the connection with the table is in the middle of the table then the leadscrew only needs to be 1/2 the table length plus supporting/machining allowance. This does mean that the end bearing in under the table and not at the end like yours. Apart from the more complex mechanical arrangement is there any other reason not to do this? I'd rather not buy any more 10mm x 2 leadscrew.
Robin - the leadscrew is whatever MarchantDice sell - carbon steel I think.
I'll admit I got a bit carried away and bought their package of 3 lengths - 400mm(X), 350mm(Y), 250mm(Z) - and 3 Delrin nuts before I really thought things through :), and I know know I could have got a better deal from Lee (may still do so), however this is my thinking so far:
I got some 16mm x 500mm rails for the table X traverse. decided to go for a fixed gantry, moving X table as I reckon I can make this more easily rigid than a full moving gantry. With 500mm rails I can get a full traverse on a 230mm table.
The 350mm leadscrew will give me about 200mm usable table width in the Y (assuming the motor mount is ~100mm wide) or I could use the 400mm here to give me 250mm usable table width (in which case I would buy another 600mm of leadscrew at £6 approx). I have some 12mm x 500mm rails which would need to be shortened as appropriate to "Travel + 125mm", i.e. 325mm or 375mm, the remaining rail being used for the Z i.e. 150 or 100mm of travel allowing for mounting.
The remaining leadscrew would give me up to 170mm approx Z travel but I will be limited by the rail length as above.
Here is a quick sketch of the base and X axis. haven't yet decided what to make this of yet... mdf or Ali...
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