Denford Starmill - replacing spindle

[andy_con]

trouble with starmill and novamill is the way the spindle motor is integrated into the head.

unless you get a replacement motor of exactly the same size you will lose z travel.

although a small machine and small motor, it will blow these cheap Chinese ally framed mills out the water, so don't put it down. can you provide some photos of exactly which model of starmill you have and any photos of motor and head if you have taken things to bits?

are you aware on certain models you can raise the head on a starmill and novamill?

[Doddy]

@andy_con:

Either solution - slaved second spindle or replacing the head housing - I'd look to leave the original spindle motor in as a dead-weight counterbalance, the new chinese water cooled spindle being directly mounted in place of the spindle (or offset). I don't see any impact on Z travel.

Re. frame, yes, it's a stiff little bugger. I'll try to get a photo over the weekend - but it's a bit of a hybrid - the previous owner removed the ATC at some point, reworked/refurbed the spindle and bearings).

Raise the head? I'm not sure I understand what you mean... maybe a photo is in order

@JAZZCNC:

With the limited y-travel I'm pretty sure that I couldn't mill the complete back bracket as a one-er, so it'd be a challenge to get the two sides to the dovetail perfectly parallel, and factoring in the gib strip. Also, if cutting steel, it's a big lump for a small machine. Maybe I'm making excuses and avoiding the hard work. I did have a quick look out for any machines being broken, and will probably keep an eye out, but these things are getting a little rare.

@andy_con (2)

I've not got to the motor - it's inside the casting, I could make an effort and break it down, but the laser/IR RPM thing I have claimed just shy of 3k.

@uli12us:

Replacing the existing spindle with a new one?, it's do-able, and probably a whole lot easier. I might ponder this option. I would prefer a much bigger collet system - ER20 or ER25 would work (and I have ER25 collets); but, it's easier to source a spindle motor than a spindle. Okay, I have a lathe, so it could be a winter project to turn a spindle myself (and somehow mount the collet holder, whilst maintaining a level of precision). Interesting option, though I fear more complex than the alternatives. I'd like to retain the strength to cut metal, so nothing too small... I'll have to go into uncharted waters and look at bearing options.

Okay, I'll try to remember to post pictures fri/sat, see if that helps ideas to converge.

[uli12us]

No not replacing, the existing spindle remains still in place, but you have a special toolholder with ballbearings in it and a small beltdriven spindle in the middle of the holder, like in some older manual engraving machines.
If I read it correct, you have a BT35 spindle. that holder should have some 38mm diametre. with a 1" bore you can have a spindle with 1/2" diametre.

[Doddy]

No not replacing, ...

Cooer, that's interesting. The Z-travel on the star mill is pretty good for such a small machine... I have a couple of BT45 toolholder that could be adapted for this. I already have a crude spindle-lock that would hold the existing spindle in place... hmmm, that's an idea that I hadn't considered, and could be appropriate for simple flat plate milling/drilling. Let me have a ponder and play...

[uli12us]

Here is a ebay auction, where you can see, what I think of it.

But the peek of the spindle, should turn 180°

http://www.ebay.de/itm/Graviermaschi...gAAOSwv-NWbloo

A part similiar to this, with an added pulley rotates inside your
toolholder

http://www.ebay.de/itm/ER11-12-x-100...EAAOSwl8NVV~vL

[andy_con]

thinking about it, the novamill has a slightly different motor, its 5000rpm.

the starmill and novamill have the same column design and size, so a novamill motor would probably fit.

problem with adding a high speed spindle is the angular contact bearings in the head. angular contact bears are open, so when they get warm/hot the lubrication runs out, so they don't last long. to work properly and last long at high speed they need constant lubrication.

ive just replaced the spindle bearings in my denford triac, with lubrication they are rated at 26k rpm. but they aren't lubricated, the stock motor in there only runs at 4000rpm so they will be fine.

[Doddy]

A photo, to hopefully explain what it is I have. As previously mentioned, ATC was removed, so the spindle has a ??? sized bolt acting as a draw bolt for the BT35 (got it wrong the first time) tool holder. This isn't a problem for me as I use a BT35/ER32 toolholder for most things (though this requires a spindle lock).




Edit: Remove the following paragraph (daft idea), replace with that, below.

The height of the material on the bottom of the head, holding the bearings, is something like 35mm, and clearly not finished to be readily used as a mount. There are some M8 holes tapped on the underside of the head which I could mount a plate (with a cut-out for the existing spindle), take that to the edge of the head and then mount a plate perpendicular as a mount for another spindle. That might be my preferred route. Would that be stiff enough with, say, 15mm 6082? Actually, thinking about it, it could be a good opportunity for me to practice my welding (got a tig, somewhere), I guess 5mm mild steel plate would be stiffer than ali (I think I need to be mindful of the weight here, can't go silly) - extended out to the front of the head with a fillet plate joining the horizontal and vertical members

Ignore the above paragraph. Next crazy idea is this: There're the ground ways on the vertical column that must be perpendicular and flat. What's stopping me removing the head, drilling/tapping and mounting supported rails to the ways (this is the only bit I'm hesitant on at this time, but this shouldn't mean that I can't recover the machine at a later time - a few tapped holes wouldn't affect the geometry of the ways?), and mounting a simply carriage, onto which would bolt the standard chinese spindle mount. That all feels very do-able, allows me to maintain the offset from the column to the centre of the spindle (so as to not lose out on the Y traverse), and is easily machinable with what I have to hand (apart from the supported rails and carriages... minor point). I'd lose the low-speed of the existing spindle, but I hate using the machine on steel (it doesn't feel strong enough, too much chatter). This is 90% inspired by Jazz's idea of replacing the head but avoids some of the problems that I envisage with the dovetail and suitable materials.

[Doddy]

ive just replaced the spindle bearings in my denford triac

Andy, assuming the head on the trial is similar to the star mill, could you walk a novice through the process of replacing the bearings?

I know I start with the lock washer, spin off the nut (which is used to pre-load the bearings?). But having been through this a long long time ago I'm pretty sure that after that nothing else wanted to come apart... what's the ideal way to remove spindle from bearings and bearings from head? I've seen the mechanical drawings (Denford's web site) - there's not much to this, but my random tugs some 12 months ago didn't offer any solution to getting to the bearings.