I'm the lucky new owner of an Alexander Master Toolmaker milling machine. It came with the horizontal overarm and arbour, the standard vertical head, the self-powered high-speed head, and a rotary table which might not be an Alexander (doesn't look exactly like the ones in the manual) but which is similar in form. It's my first milling machine, and I'm really looking forward to getting acquainted with it!

However as it stands it has the massive two-speed 415V main motor. The motor is in good condition, but generating 415V three-phase for this one machine looks a bit silly cost-wise compared with a new dual-voltage motor and VFD, which would also get me a soft start and (if I ever needed it) finer speed control. I know that other folk have done this kind of conversion – so, is there anything I should be aware of? I imagine I'll need to machine a new pulley and find a way to mount the new motor. Ideally I wouldn't make any irreversible modifications. Any tips? Bear in mind that I probably won't have a mill, though in a pinch I could drive the old motor off 240V at 29Hz to take part in its own replacement.

The other thing is that the high-speed head appears to be the older pattern that takes U2 collets but with the 14.5×1.2mm Löwenherz thread. (I haven't confirmed that for sure just yet.) It came with no collets. My immediate thought is to grab a bit of EN16T and make an ER20 collet chuck with an outer profile and drawbar thread to match the U2 profile, which should be within my capabilities. Is this a bad idea for some reason I haven't considered?

I'm a relative newcomer to this wonderful hobby, so any advice from those with more experience than me would be gratefully received.

Many thanks!

Thanks, I'd figured out the tramming process but the brake disc is an excellent tip.

That's good to know! Did you have to fabricate a new motor mount, and if so do you have any tips? I was thinking of getting some bits of 15mm steel laser cut and welding them up. Also did you retain the two speed arrangement, and if so how? I'm looking at perhaps using a 6-pole motor and running it at 37 or 75 hz to get the two speeds.

I'll need a bit more than an adapter plate – it's hard to overstate just how huge the existing motor is, for a 1.5hp motor it is absolutely massive. A modern 2hp (1.5kW) motor is so much smaller that I'd need to raise the mounting foot by about 50mm to avoid having to fit longer belts and modify the belt guard! That's why I'm thinking of fabricating a new mount as being the path of least resistance.

Size is one of the reasons I'm considering a motor swap, the motor sticks out quite a bit at the back of the machine and I'll save a few inches in a cramped garage if I swap to a smaller unit. The other reason, frankly, is cost; I can get a new motor and VFD for less than the cost of a decent (i.e. digital or rotary, not static) 415V phase converter. Crazy but true. If I do the swap I'll keep the old motor and make sure I do nothing irreversible though, I like the idea of being able to restore the machine to "as built" condition.

Hi Martin,

As far as I have been able to ascertain, the "normal" 16mm U2 collets have a full M16 thread whereas the collets that the Master Toolmaker uses have a weird 14.5mm 1.2mm pitch Löwenherz thread. I'm going to have a go at cutting such a thread on the end of a bit of scrap aluminium (on my imperial lathe, should be fun) to check that that's what the captive drawbar accepts – I can think of no other way of finding out short of disassembling the spindle! I could keep my eyes open for the correct U2 collets but I already have a full set of ER20 so an adapter seems like an attractive idea if I can make a decent one.

By the 'quartering' table do you mean the table that's angle-adjustable? If so yes, it's the only table I have (and it's actually adjustable in 3 axes, it swings and it tilts both ways). I can think of several applications for it, though as others have pointed out, it might take me a while to become proficient at tramming it quickly if I do make use of its adjustability! The previous owner of this machine also did a couple of larger jobs without the table, bolting work directly to the T-slotted vertical 'table' (apron?) to which the horizontal table attaches. Lots of possibilities.

I'd assumed that a new brake disc would be ground flat and parallel, to avoid noise and vibration on braking, is that not the case?

Andy

Thanks! No idea where I'd find a bearing ring. I'll keep my eyes open though.

I'd thought of machining the ER taper first with the part choked up in the chuck (the blank will fit down the spindle bore) and making up a plug gauge with an accurate centre hole, so that when it's finished being a gauge I can fit the plug into the ER taper and then turn the remaining features between centres. I like turning between centres because, as an "ambitious beginner", it allows me to take the part out of the lathe and test fit threads and tapers without losing my setup or needing to invest in more measurement equipment! Let me know if that's a bad idea for some reason I haven't thought of. And yes, I'm a big fan of plug gauges and "go/no-go" gauges and things like that. As a hobbyist I have more time than skill, might as well make that work for me. Any ideas for getting a good finish on the collet taper would be welcome – can't really lap a cone, and I don't have a toolpost grinder.

My information on the thread profile came from an old Practical Machinist thread on the GHA high-speed head. The collet is referred to as a Lorch B, and the weird thread is discussed at length. It might not be correct though!

Andy

Thanks Martin!

I'd also thought of relieving the rear portion of the U2 taper on the adapter so that it only seats near its outer edge. My thinking was that it's not actually closing a collet, it's just ensuring concentricity and providing lateral stability, and so I'd rather ensure that the tapers definitely meet near the end than risk a poor fit in the other direction which would lead to the contact between the spindle and adapter effectively being further from the tool. If that makes sense.

The high-speed head accepts very significantly smaller cutters than the regular head yes, the regular head being MT4!

Thanks for the info Simon – I've measured the bore on the high-speed spindle and it's a shade over 16mm so they're definitely not the same. The best lead I have so far suggests that the drawbar thread is likely to be 14.5mm x 1.2mm pitch Löwenherz (53° 8′ pitch angle), but other 16mm U2 collets do seem mostly to have a full 16mm thread or else a sawtooth thread, so I guess I'll just have to experiment until I find a thread form that fits – I can't think of a way to measure the captive drawbar thread. Doesn't help that there's a key in there too so I can't just thread the end of a bit of bar and see if it fits, I've got to cut a keyway too (although I suppose for a quick test I could just hack away enough material to avoid the key, rather than cutting an accurate keyway).

I'm still holding out hope that another owner of a GHA high-speed head will pop up and tell me definitively what the necessary thread form is! 😀

Andy

Extremely helpful, thank you Phil! The drawing would be great, and I'm perfectly happy to wait – with work and a young family I can be in no hurry.

My HS head also has a three-phase motor but it's dual-voltage, unlike the main motor, so I too plan to fit a VFD.

If you have any photos of your modifications, including the mounting of the main motor and the Poly Vee conversion to the HS head, I'd be interested to see them. No rush, though.

Is that a brake rotor mounted on the legs, or is it something else that you trust to be flat?

Andy

Edited By Andy Pomfret 1 on 21/05/2021 16:03:06