Denford Starmill - replacing spindle

[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.

[andy_con]

remove all tools and tool holders from the spindle

you will need to fold down the tab on the tab washer that's stopping the tab nut from turning. undo the tab nut and remove, remove tab washer. remove belt, undo pulley, probably two grub screws locking it to pin. remove pulley and pin.

id have to see a photo of how the bearings are sat around the spindle.

but there is probably a guard on the underside/spindle on the head to prevent crap from getting into the bearing, you will need to remove this. normally 4 allen key bolts.

once all the above is done and subject to how the bearings sits you may be able to tap the spindle down/out with a hammer. but use some wood so you don't damage the spindle. also put a car jack or something on the table to support the head whilst tapping with a hammer. you don't want to snap the z belt and have the whole head crash into the table.

[andy_con]

http://www.denfordata.com/bb/viewtopic.php?f=41&t=3585

[Doddy]

Just an update

I decided to bolt two rails onto the dovetail and mount a sled onto those, with a bracket attaching the base of the sled to the orginal Denford Z-axis positioning plate.


Picture 1, shows the basic sled, provided curtesy of a member on here in response to an RFQ.

(Also, the neodymium magnets on the right rail tells the tale of my hand-drilling the cast iron of the original dovetail)



Picture 2 shows the spindle mount attached to the sled. An early picture - was yet to be wired (the copper pipe in the background suggests the minor distraction of replacing an indirect-heated cylinder that was leaking, that somewhat halted play on the mill).



Elsewhere on the site I've discussed the problem with wow/flutter on the spindle, ultimately overcome with using RS485 between the computer and the Spindle Controller. At this time everything works as I'd hope it to.

[magicniner]

That's looking tidy, have you mounted the new spindle to give the same throat as the old one?

- Nick

[Doddy]

More by chance than design it sits within a couple of mm of the original spindle