Author Topic: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine  (Read 11380 times)

Offline andyf

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The original induction motor on my 40 year old Dore Westbury milling machine motor often needs a yank on the pulley belt to get it going, and some of the internal insulation looks a bit dodgy. The machine is the Mark 1 shown in the third and subsequent pictures at http://www.lathes.co.uk/dore%20westbury/index.html . Stepped pulleys give three speeds and an 8.8 to 1 epicyclic gearbox can be engaged/disengaged to give six speeds from 35 to 1360 rpm. I thought I might try a variable speed motor for greater flexibility. According to our US brethren, DC treadmill/running machine motors are ideal for this sort of project. Old ones seem common as dirt in the US, but are rarer in the UK.  

However, Ebay revealed "Running Machine. Faulty - runs for 10 seconds, then stops”.  Only 3 miles away, and £15 secured it. Back home, it took five minutes to find the little magnet for its speed sensor stuck to the steel frame and return it to the pulley where it belonged. After that, it worked perfectly. I feel a bit sorry for the seller, who had ordered a new one for about £400.  I climbed on and achieved a dignified canter, but the novelty only lasted five minutes, so I started dismantling it. Here it is cluttering up a corner of the kitchen, before I took it to bits:




And here’s the rating “plate” from Leeson in Wisconsin, USA. 220V x 6.5A = 1430W, so 2HP is slightly overstating it.
 

I hadn't realised there was another Wisconsin in China.....

Speed was varied by pressing the buttons shown in the first pic. Fine for a treadmill, but hardly ideal for milling. Also, the control board was an inconvenient 12” x 9’’, and the separate “power” board about 6” x 7”. I experimented a bit with streams of control pulses from optical choppers out of an old computer mouse, but results were unreliable. Departing from my usual miserly approach, I forked out £70 for a brand new KBIC 240 controller from a nearby stockist. Input is 230V AC (the UK domestic supply) and PWM output is 180V DC. OK for 2HP motors, when used with a heatsink. 2HP is overkill for this size of machine, so I don’t think the “undervoltage” will make any practical difference. The stockist didn’t have the “official” £20 heatsink to bolt under the aluminium frame on which the board is mounted, and in any case underneath didn’t seem the best place for it. I bolted a couple of salvaged heatsinks to the upstand at the end of the frame, directly behind those semiconductors which were likely to get hot. There was no sign of heatsink compound anywhere, so some was added.
 


The scrapbox also yielded a diecast aluminium box of the right size to accommodate the board. I cut a rectangular hole into one end of it so the heatsink could stick out and get some air.

There was room left in the box to fit a potentiometer speed control and a home-made “no-volt” switch comprising a 13A mains relay with a push to make switch to actuate the relay coil, wired so that the coil would hold itself on until the circuit was broken by a push-to break switch, or by a mains power failure. The switch buttons are the usual green for go, red for stop colours.



On the bench, I temporarily hooked up the new control box to the motor and gingerly plugged this ensemble into the mains. Success  :thumbup: :thumbup:  Zero to warp speed and back again at the twist of a knob. And with the low-speed pulleys and 8.8 to 1 epicyclic gearbox brought into play, torque should be high enough to bend the mill column  :lol:.

So all (!) I now have to do is:
1. Remove the 12lb/5Kg cast-iron flywheel from one end of the new motor’s shaft, and replace the
    pulley on the other end with the 3-step pulley from the old motor. The bore in this would need enlarging by about
    5 thou from 0.625” to 16mm.  
2. Fix the new motor in place of the old one.
3. Attach the control box in a convenient position - probably on the spindle head.
4. Wire up properly, with regard to safety.
5. Arrange some way of calibrating the control knob to give the particular spindle speed required for the job in hand.


Andy

Edited to fix a missing pic


« Last Edit: February 03, 2010, 06:54:25 PM by andyf »
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline John Stevenson

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #1 on: February 02, 2010, 06:42:01 AM »
The cast iron flywheel is threaded on with a LH thread.

John S.
John Stevenson

Offline andyf

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #2 on: February 02, 2010, 07:03:30 AM »
Thanks for the tip, John. This one isn't threaded, though - there's a key and two grubscrews, one bearing on the key and the other at 90 degrees round the shaft. It's off now, and will come in useful for something or other, sometime. The Poly-V pulley on the other end of the motor is going to need a bit of persuasion.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Bernd

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #3 on: February 02, 2010, 10:41:27 AM »
Andy,

Here's a pic of using a tread mill motor to power an old Buffalo Forge drill press. Used to have a 1HP 3Phase motor on it. Now it has a 1HP DC tread mill motor powwering it. I used the orginal electronics since they were a lot less complicated than the more modern one. I've got 3 more motor assemblies for some of my other machines I plan on putting DC motors on. Anyway here's a close up pic of the drill press mounted motor.



I did a thread on moving this drill press from the garage to the basement here: http://madmodder.net/index.php?topic=362.0

Bernd
You can't fix "STUPID".

Offline andyf

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #4 on: February 02, 2010, 11:29:38 AM »
Nice one, Bernd. It looks a bit  :zap: though I'm sure you've made it safer since your pic. I've put my circuitry in a box so the electricity can't fall out.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Bernd

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #5 on: February 02, 2010, 10:18:05 PM »
Ah well..... I ah......... not yet. No excuses. Just that darned round tuit the keeps me from finishing projects. :bang:

Bernd
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Offline andyf

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #6 on: February 03, 2010, 05:54:30 AM »
Yesterday, the job progressed a bit further, but my efforts ended with a bit of a disaster.

I needed to get the flywheel and poly-V pulley (both keyed) off the new motor, and attach the 3-step pulley from the old one. The flywheel came off easily, but the pulley needed persuasion using bolts and the long nuts from a clamping kit as jacks. The 3-step pulley from the old motor was easy to slip off its keyed shaft, but there was no keyway in the pulley itself. It was secured by a grubscrew going into the keyway in the shaft. I’m wondering if I should bother cutting a keyway into the pulley. The grubscrew method seems to have lasted 40 years without any problems.
 
The pulley was held in the 4-jaw and persuaded to run true. I couldn’t find either a suitable boring bar or the one I once improvised by grinding up an Allen key, so I used one of the good teeth left on a damaged ½” endmill to enlarge the bore from 5/8” to 16mm.


 
Next: mounting the new motor. Originally, it sat in a pressed steel cradle, but this couldn’t easily be modified to fit on the mill. The cradle on the mill is a casting, but contoured to fit the old motor which was about 1½ “ more in diameter than the new one. Reprofiling was needed, so I resorted to JB Weld. The previous night, I had wrapped my new motor in kitchen clingfilm to enable release, and stuck duct tape on the parts of the cradle where excess epoxy would need to be trimmed. JB Weld was applied liberally to the cradle, the new motor was given a good push down into it and left there overnight. In the morning, I removed the rolled-up paper plugs which had been put in the cradle’s four bolt holes, drilled the holes clear through the epoxy coating, and trimmed off the excess.

Of course, the original threaded fixing holes in the new motor casing were in the wrong places, and only two had been needed when the motor sat horizonally. On the mill, it would be vertical and two M8 bolts might not be sufficient, so the next task was drill and tap four new holes in the casing to match the cradle. The motor was taken apart so I could later clean swarf off the permanent magnets fixed inside the casing. Two of the holes were easy – they could go right through, in one of the gaps between the magnets. The other two holes were over one of the magnets, so are shallow and only allow about three threads of engagement for that pair of bolts. Still, adding another two slightly dodgy fixings to two good ones can do no harm.

I fitted the motor to the modified cradle, and bolted the cradle to the hinged arrangement which tensions the drive belt. The big boss expands inside the cross-tube of the mill, and the lettering on this photo is explained later.



Then I fixed my electronic floggle-toggle box to the mill. The spindle head has a couple of tapped holes on the front for fixing the pulley guard. I bent up and drilled some crap DIY store 4 x 20mm flat stock so I could bolt one end to the spindle head, and the other to the flange on the other end of the Dore Westbury’s cross-tube. The next pic shows this, with my box of electrickery fastened to it – the photo has been crudely edited to erase a confusing background, and the pulley and gearbox are chocked up to improve the view. The pulley guard is missing, but will return. I don’t want an unguarded drive belt, particularly at eye level.



The motor was mounted on the Dore Westbury and the wiring temporarily hooked up for a test run. All went well at first. The combination of the 3-speed pulley drive and the variable speed motor gives a range from dead slow to whirling round far too fast for the spindle bearings.

An earlier photo is repeated here, for convenience:

The hole for the bolt through lug A on the swinging plate has a lock-nut on it below the lug, and a conical end which goes into a correspondingly shaped hole on the fixed plate with the big boss sticking out of it. There’s a similar lug and bolt below, so the fixed plate is pinched between the two bolts, which act as a hinge. The black ball-handle turns a bar which is eccentrically hinged between lug B and a similar lug below, again using cone ended bolts. The bar acts as a cam to tighten up the drive belt.

Testing came to an abrupt halt when the motor, cradle and swinging plate fell off the hinge :bang: :bang:. It’s lucky the motor wasn’t running at the time, or there would have been mayhem. I thought I had located the hinge bolts properly in their holes; all seemed solid enough when given a good tug, but one of them must have missed its hole and have bitten just deep enough into the painted aluminium surface to hold temporarily.  :bang: :bang: repeated ad infinitum....

The only damage was that lug B broke off when it hit the edge of the bench on the way down. The cable to the motor acted as a safety line and stopped its headlong plunge just short of the concrete floor. Things could have been worse – it might have been lug A which broke. That one takes the weight of the motor, whereas lug B isn’t subject to much strain.

So, yesterday afternoon’s work ended with re-attaching the lug using two steel dowels and more JB Weld.  I’ll play safe and wait until this afternoon before disturbing it.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline andyf

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #7 on: February 03, 2010, 05:00:35 PM »
Things went much better today  :D. This afternoon, yesterday’s JB Weld and dowels repair had hardened after 24 hours basking in the warmth of the house. The reattached lug seems good and firm.

Because the cable had stopped the falling motor before it hit the floor, I dismantled the motor again and inspected the wires within. No apparent damage, but to be prudent I replaced the shortest wire, which will have taken the strain.
 
I continued on electrical safety by drilling and tapping holes to fix PVC brush covers in place of the originals. In the treadmill, the motor had been covered up and the original plastic brush covers were simply sprung into place. They could easily be dislodged.

More drilling and tapping provided fixing holes for a plastic box in which to cram the wires which emerge from the motor, the EMC ferrite ring they take a turn through, and the connector block coupling them to the DC supply cable from my control box.



Both the motor frame and the body of the control box (and thus the whole mill) are connected to earth (ground). That might prevent a short circuit causing a fire by blowing the 13A fuse in the mains plug, but it would only need a few tens of milliamps to kill me off. To protect myself (famous last words!) as far as I can from a major :zap: the supply to my entire shop runs through an RCD.

Earlier this evening I was ready for further tests. Having made doubly sure that the motor was secure (I do learn from my mistakes!) I did some speed trials using my only tacho, a pushbike speedo reading up to 2000 rpm. To actuate it, I cobbled up an arrangement with a magnet held in a slitting saw arbor in the spindle. With the drive belt on the “low speed” pair of the 3-step pulleys, the control knob gave speeds from 0 to 820 rpm. Using the medium-speed pulleys, I got 0 to 1820 rpm. Anything much faster would be beyond the range of the tacho, so I backed off until the spindle was at 910rpm (half of 1820) and stopped the motor with the off switch, leaving the knob where it was. After moving the belt to the high-speed pulleys, I switched the motor back on. Spindle speed was now 1810 rpm. If that’s half speed, top speed would be around 3600 rpm – way too fast for my old machine. Apart from anything else, that big epicyclic gearbox is sure to be slightly off-balance. For comparison, maximum on a Sieg X3 is around 2000 rpm, so I think I’ll forget the high-speed pulleys.

For really low speeds, I can bring the 8.8 to 1 gearbox into action.  :smart: Arithmetic shows that the maximum speeds in the two ranges would then be around 90 and 200 rpm.

There’s nowhere on the spindle to fit a magnet or optical stripe to actuate the sensor for a tacho. I’ll have to fix up an rpm dial for the speed control knob, using a temporary tacho as above to calibrate it. The specs for the control board say that speed regulation under varying loads is within 1%, so a dial should be accurate enough.

One nice feature is the soft start on the new motor. Previously, the shop lighting dimmed for an instant when I switched on, but that isn’t happening any more.

I’ve given a bit of thought to a cooling fan. In the treadmill, the motor was horizontal, with a plastic fan on its shaft. The fan broke during removal of the original pulley. Now the motor is vertical (I hope its bearings are happy in that orientation) convection will help, and a fan on the shaft wouldn’t do much at low speeds.  I’ll check how hot the motor gets, but I don’t expect trouble. The old motor was only about ½ or ¾ HP, so 2HP is overkill and should run cool.

I wanted to end with a pic of the complete mill, but my camera batteries have just given out. so that’ll have to wait until the morning for recharging.

Andy.
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline CrewCab

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #8 on: February 03, 2010, 05:37:07 PM »
Nice thread Andy, thanks  :thumbup:

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Offline andyf

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #9 on: February 04, 2010, 12:50:19 PM »
Here’s a pic of the entire machine with its new motor, control box and the car fan belt I had to get – the new motor being a different diameter, the old one (also a fan belt) no longer fitted. The local car accessory place was very understanding, letting me borrow a selection so I could pick the best size.  This photo isn't the best size, though:



Apart from concocting a dial for the control knob so I can set the spindle to a chosen speed, the project is complete. Actually, as there are two useable speed ranges on the pulleys (the third is dangerously fast) and each range can if desired be geared down by the epicyclic gear box. I’ll probably end up making a little frame like those for labels on filing cabinets, and four different dials to slot into it.

Speaking of the epicyclic box, this is in the big canister on top of the spindle head. I found it quite interesting when I got the mill and looked inside. It uses six Myford changewheels, and no internally toothed gear. Very cunning.

If you have been, thanks for reading.

Andy.
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline CrewCab

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #10 on: February 04, 2010, 02:02:47 PM »
As I said above Andy, a good read, and ............. it's nugget's like this that keep it entertaining  :thumbup:

I've put my circuitry in a box so the electricity can't fall out. 

CC

Rob.Wilson

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #11 on: February 04, 2010, 02:20:47 PM »
Hi Andy

Very neat job ,looks great on the mill  :clap: :clap: :clap:

Cheers Rob

Offline andyf

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #12 on: February 04, 2010, 03:31:51 PM »
Thanks, guys. It's been fun. I'm quite fond of the Dore Westbury, even though it's a bit of an old crock and the round column (which goes down through a hole in the benchtop) causes problems.

First, to raise/lower the head, you have to unclamp the column at the bottom, and jack the column up on its screw thread using the round nut with tommy bar holes in it. This leaves the head free to swing in an arc, so all registration is lost. Changing from a long drill to a short milling cutter sometimes ends with a lot of resetting. I think this applies to most round column machines.

Secondly, you can't be too ambitious with cuts, because lack of rigidity in the column (which is a thick-walled tube) can cause problems if the head is particularly high. I've read that filling hollow columns with epoxy and granite chips can help. Or maybe I could stiffen it up by cramming it full of the blue pills the inhabitants of my spam box are so anxious I should buy....

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Bernd

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #13 on: February 04, 2010, 05:38:48 PM »
Very nice retrofit of an old mill. Almost looks like it belongs on there.

Bernd
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Offline CrewCab

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #14 on: February 04, 2010, 05:44:51 PM »
I could stiffen it up by cramming it full of the blue pills the inhabitants of my spam box are so anxious I should buy....

If you run short we can probably all chip in  :coffee:

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Offline Ned Ludd

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #15 on: February 07, 2010, 07:59:45 PM »
Hi Andy,
With regard to your round column and loss of registration, have you thought about using a laser level mounted on your mill head, pointing to a vertical line on the far wall of your shop. If you have a Pound shop near you, they can be bought for, surprise, surprise, a Pound, less batteries of course. You don't get much for a Pound these days do you? :(
Ned Ludd
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Leafy suburbs of NW London

Offline andyf

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #16 on: February 08, 2010, 05:33:37 AM »
Thanks, Ned. I got a laser from the local pound shop with exactly that in mind, but on thinking more about it I went no further. There were three problems:
1. The best wall for the job is obscured by tools hanging from racks and hooks.
2. The mill sits on a stand which can shift in position slightly on the floor if I bump into it during the course of a job, 3. A round column, though it can be a nuisance, does have one benefit. The ability to swing the spindle in an arc from side to side sometimes enables me to get the spindle over the extreme ends of the table and beyond, in effect extending the X axis travel of the table. This can come in useful, but to use a laser it would mean drawing an exactly vertical line down the wall every time I changed the position of the spindle along its arc (perhaps, rather than "exactly vertical", that should read "parallel to the column", which would make the line more difficult to draw). 

For Sale: Laser, as new. £0.99, batteries extra.  :lol:

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline DMIOM

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #17 on: February 08, 2010, 08:08:56 AM »
Andy,

have been in the same dilemna with my manual Warco round-column mill.

I too though at first I could have a static vertical line and always keep the laser on it - but found that (since the stand isn't bolted to the deck) it does walk around a bit.

What I came to realise is that the laser/line alignment doesn't need to be absolute & permanent - it just needs to remain consistent whilst you're elevating or lowering the head.

Mine stays reasonably consistent, but before I start moving the head, when I switch the laser diode on, I either say "OK, its on the line" or "its 2/3 right of the line, 1/3 left" and I know I just need to get it the same when I've finished moving the head. If its a long way off, I either swing the machine or the laser. I have come to learn that once I tighten the column clamps, it will move by about 1/4 a spot width! 

The further you can get the line away from the laser, the longer the light-lever and the more sensitive the alignment; I use a commercial laser diode and a plumb-line at about 3m and I find it does a good enough job.

Dave

Offline Darren

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #18 on: February 08, 2010, 08:19:29 AM »
I like the plumb line idea, KISS .... always the best  :clap:
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline andyf

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #19 on: March 08, 2010, 08:38:02 AM »
Final update: I made a plastic holder with a transparent front into which I could slip different dials to suit various pulley/gearbox combinations, and got as far as calibrating a dial. Then  :bang: :bang: I realised that it would after all be possible to fix the actuating magnet for my bike speedo/tacho, in the recess on the underside of the gearbox casing, I salvaged the little magnet which triggered the running machine’s speed sensor from one of its pulleys, together with the counterweight dummy magnet, made little housings for them from scrap white plastic, and attached them under the gearbox.  The tacho’s sensor head (the part meant to go on the front forks of a bike) was fixed to the rear of the spindle head on a bit of bent metal, held by two existing bolts.



The display works fine when the gearbox isn’t being used and is rotating as a single unit. When the gearbox is in action, its casing and the magnet fixed to it are immobilised, so the tacho doesn’t work. I doubt if there will ever be much need to find out the exact speed of the spindle in low gear, but just in case I have retained my dial holder with a simple dial, showing arbitrary markings. With the gearbox out of action, the tacho can be used to set the speed at 8.8 times what I want and the dial reading noted. Then, the gearbox can be engaged and the dial set to the same reading to get low speed more or less right.
Here’s the tacho in action. It can be hard to read if light falls on it at the wrong angle,  so it is on a bracket allowing it to be swivelled for a better view. 105.2 kph = 1052 rpm (and it thinks I've cycled 5.65 km this morning!). Sorry these photos are so big.

 

The tacho looks a bit out of place, but it's convenient having it just above the control knob.

If I want 120 rpm using low gear via the 8.8 to 1 gearbox, I would set the machine to run at 1052 rpm or thereabouts, stop the motor, set up the gearbox,and wind the motor up to 8 on the dial again. The tacho would read zero, but 1052/8.8 = 119.4, which is near enough to 120. 

Footnote: To turn it into a tacho, a “bicycle computer speedometer” should be programmed as if on a pushbike with wheels of 1667mm circumference, and to read in kilometres per hour. The reading x 10 then represents rpm. Mine (an “Echowell Star” at £9 from Halfords here in the UK) reads to one decimal place up to a maximum of 199.9 kph/1199rpm. It only updates about once a second, so a moment’s pause is needed after altering speed, to let the reading settle down.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline NickG

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #20 on: March 09, 2010, 03:41:45 AM »
Very nice work Andy, looks as though it will be much more useful now.  :thumbup:

Nick
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Offline madjackghengis

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #21 on: March 09, 2010, 11:03:16 AM »
Thanks, Ned. I got a laser from the local pound shop with exactly that in mind, but on thinking more about it I went no further. There were three problems:
1. The best wall for the job is obscured by tools hanging from racks and hooks.
2. The mill sits on a stand which can shift in position slightly on the floor if I bump into it during the course of a job, 3. A round column, though it can be a nuisance, does have one benefit. The ability to swing the spindle in an arc from side to side sometimes enables me to get the spindle over the extreme ends of the table and beyond, in effect extending the X axis travel of the table. This can come in useful, but to use a laser it would mean drawing an exactly vertical line down the wall every time I changed the position of the spindle along its arc (perhaps, rather than "exactly vertical", that should read "parallel to the column", which would make the line more difficult to draw). 

For Sale: Laser, as new. £0.99, batteries extra.  :lol:

Andy
Andy, when I was working with a bench top mill, I often needed that extra X axis work space you claim from your round column.  I still needed to be able to keep the head in alignment at other times.  I found that the easiest way is to hang a plumb bob with lots of chalk on the line, and use it for the line, and hang it from a pipe or beam so it could be moved easily when I needed a different line.  It also ensures a true vertical line as well.  It never failed me as long as I had that bench top mill, and having more than one meant I could use both the added X axis and have an accurate alignment at two different head positions and move between them, to machine long work.  Mad Jack :ddb:

Offline andyf

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Re: Fitting a Variable Speed Motor to a Dore Westbury Milling Machine
« Reply #22 on: March 09, 2010, 03:59:10 PM »
Thanks, Jack. Ned made a similar suggestion, and I'll have to revisit the idea. I did buy a laser, but it was a real cheapo - too big a blob of light to be much use. l may have a problem getting the mill column as vertical as the plumbline, though. The mill is bolted to a small (1'6" x 2' square table) which stands on a sloping (1" in 4') concrete garage floor, across a corner. The table legs are of different lengths, so that the column is more or less vertical if the whole thing is positioned exactly on some marks I made on the floor, but any movement (and I do have to move it quite often, to get at things which have dropped behind it) can throw the alignment off. I suppose a patch of self-levelling floor screed would be a good idea.

But it's surprising how far you can get with a bit of planning. I've learned to hoist the head higher, and extend the quill further down, than is strictly necessary for things like a short centre drill, if the next step on the same hole will involve a longer drill bit.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short