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)
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.!
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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.
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?
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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.!!!
also what does it say on the side of the motor as I'm pretty sure my starmill is 4000 rpm
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.
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.
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.
Last edited by Doddy; 18-12-2015 at 12:36 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.
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