View Full Version : Denford Starmill - replacing spindle

17-12-2015, 06:55 PM
I have a Denford Starmill, converted by previous owner to Mach3.

The spindle is belt-driven from the motor hidden in the column, and can be adjusted upto around 3000rpm.

The last time I used it it popped the circuit breaker a couple of times before settling down okay, whenever the motor span up - something of a concern! That, coupled with the pretty low rpm (I'd like to use the machine for PCB drilling/milling, and would prefer to get up to 24k rpm) has lead me to think of the chinese water cooled spindles.

The existing spindle is held in place with two 80mm dia (ext) bearings, with belt drive to the motor. The spindle tooling is the old BT45 style, for which I have a ER32 collet holder. All that I can live without.

One thought I had was to remove the spindle and bearings, disconnect the motor, remove the bearings and bore out the circular rib (somewhat less than 80mm dia) that holds the bearings apart, then fit a 80mm chinese spindle motor in situ, directly driven (no belt) with some form of bracketry. But, boring the rib might be a challenge! (depending on the weight/shape I might get it in a 4-jaw on my ML7).

Another thought was a narrower bore spindle motor that would slide in with the rib in place, and turn a top and bottom sleeve to hold it in place (essentially replacing the old spindle bearings).

Is this a sensible idea?, or plain crazy? The mill at this time is good for steel (which I do very little of), but very slow for ali and next to useless for PCB - I've not got the space to realistically host two machines, so I need to make this a practical single machine.

Any advice, gratefully received. (or any pointers to a cheap [<1k] alternative)


17-12-2015, 08:48 PM
I wouldn't bore the head housing unless you can still buy them.? It would be an easy thing to make a new head unit just for the WC spindle and remove old Spindle head completely. That way it can be put back if required or when sold.

Other option is to have WC spindle Offset in a bracket on the head so have dual spindles. Obviously you'll lose some travel with this which on such a small mill might be problem.? You'll also probably have assist the head with a Gas strut or counter balance to help with the extra weight.!

17-12-2015, 09:01 PM
As always, solid advice. I had thought of slaving a second spindle on the side of the column - the bed is over-long for the available travel, so that might be feasible (I thought it originally too silly, but to have another suggest it gives me more confidence). Only problem is the available height of material (cast iron?, I think) to mount the motor bracket is around 20mm, and I'd have to be careful not to drill/tap into the bearing that it holds... I could probably fit an additional stabilising bracket higher up the enclosure... I'll think about that.

A new head housing?, Hmm, I need to get into the shed tomorrow (maybe saturday, drinks with the lads tomorrow) to have a look at that. I won't be able to machine that myself, but I've had satisfaction with help given by others on here before now.

I'm thinking, I've got stock in the shed to make a couple of custom mounts so I might tinker with a second/slave spindle in the first instance.

Thanks Jazz.

17-12-2015, 09:27 PM
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?

17-12-2015, 10:00 PM
A new head housing?, Hmm, I need to get into the shed tomorrow (maybe saturday, drinks with the lads tomorrow) to have a look at that. I won't be able to machine that myself, but I've had satisfaction with help given by others on here before now.

Why not it's only back plate with a simple pocket then a Dovetail cutter up the sides and you have a working Mill to make it with.?

Then just space the Spindle off the back plate. Go the whole hog and space it off with Rotary table and you'll have capabilty to machine on 3 sides.!!!:thumsup:

17-12-2015, 10:30 PM
also what does it say on the side of the motor as I'm pretty sure my starmill is 4000 rpm

17-12-2015, 11:43 PM
What, if you built a special toolholder with small ball bearings they are capable of some 30.000 turns.
In this you have a small spindle with ER11 or so collets.
On the outside you have a small pulley. then you only need a standard motor with a big pulley 10 times the diametre of the small pulley and a belt as link between them.

18-12-2015, 12:11 AM

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


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.


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.

18-12-2015, 01:04 AM
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.

18-12-2015, 07:26 AM
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...

18-12-2015, 09:35 AM
Here is a ebay auction, where you can see, what I think of it.

But the peek of the spindle, should turn 180


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

http://www.ebay.de/itm/ER11-12-x-100-Spannzangenfutter-Zylinderschaft-mit-Spannschlussel-/321941637813?hash=item4af5378ab5:g:XbEAAOSwl8NVV~v L

19-12-2015, 07:01 PM
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.

20-12-2015, 08:00 AM
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.

20-12-2015, 08:14 AM
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.

20-12-2015, 10:57 PM
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.

21-12-2015, 04:10 PM

04-04-2016, 10:25 PM
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.

04-04-2016, 11:20 PM
That's looking tidy, have you mounted the new spindle to give the same throat as the old one?

- Nick

04-04-2016, 11:22 PM
More by chance than design it sits within a couple of mm of the original spindle