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BCA jigborer motor

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Matt Mackeson19/12/2020 14:26:59
10 forum posts
4 photos

Hello all,

I have recently acquired a nice BCA mk3 Jig borer that I am looking to get running in my home workshop. It currently has the old 3 phase 380/420v motor attached. I am having trouble trying to figure out a replacement dual voltage 3ph or 1ph motor with the same bolt patter ( 5 1/2'' x 3'' to mount in its place. ( I have very limited knowledge of such things)

I know there are a few BCA owners on here so was wondering what solutions others had used.

Any advice would be much appreciated.


HOWARDT19/12/2020 15:33:49
799 forum posts
28 photos

Motors are sized to standards, have a look at the motor and it should have a frame size such as D112 as a metric or a Nema size such as 48. Metric sizes relate to shaft height. Depends how old the machine is but metric motors have been in use in the UK for most of my working life, 50+ years. With the details you can then look at motor manufacturers sheets to choose a motor. Alternatively as some will say get an inverter.

not done it yet19/12/2020 15:43:55
6438 forum posts
20 photos

Can you not either convert or get it converted to 220V operation and then use a VFD to drive it?

My second motor conversion in the last couple of months, from star-only to delta, is sitting at my feet awaiting completion. It’s not a difficult job, although for some motors it may not be easy or even possible.

AStroud19/12/2020 15:50:48
26 forum posts
8 photos

Mine came with a 1ph motor fitted (3kw !!). It had been fitted by someone drilling mounting holes in the column about 5 1/2" down from the top mounting holes and I am guessing they must be tapped. Spacers are used to align with the pad. Otherwise I would have thought an adaptor plate would suffice.

Edited By AStroud on 19/12/2020 15:51:05

Michael Gilligan19/12/2020 16:05:46
19285 forum posts
960 photos

When I bought mine [about 35 years ago] it came with the original 3-phase motor and [at that time] I couldn’t find anyone interested in converting it .... so when I went to see Mr Godfrey at Tenga Engineering, I left it with him in case anyone needed a spare.

I fitted a 1/4 HP single phase motor, using a ‘temporary’ adapter plate [thick plywood] and have never yet found the need to change it.

One day, when all the other jobs are done ...


John Haine19/12/2020 16:54:09
4272 forum posts
251 photos

Matt, if you can, much the best approach is to fit a VFD and use the existing motor. It is presumably connected in "Star" for 380-420 V but to use a standard low cost inverter it needs to be changed to Delta. If the motor star connection point, where the three windings are connected together at one end, is brought out to the terminals, this is very easy. You should find that the cable enters the motor at a junction box with a screwed on cover - remove this and take some photos of what is inside, showing the terminals and the existing wiring. Also take a photo of the rating plate on the motor which states the voltage, hp, current, speed and that sort of stuff. If we are lucky it will also indicate if a delta connection is possible. When you have photos post them here and we can advise if the conversion is straightforward.

Clive Foster19/12/2020 17:03:36
2882 forum posts
104 photos

Mine, albeit carrying a Sigma branding, had the motor mounted on a clearly home or shop brew L bracket somewhat after the fashion of that shown in the Ultra pictures on Tonys website **LINK** . I don't recall whether the column was extended for the pivot bolt hole as per the Ultra or whether a stout flat plate had been bolted to the original motor mounting holes. The motor in question was end mounted with bolts going directly into the end bell rather than flange mounted like the one shown on the Ultra pictures.

If the mounting geometry had been correctly thought out it would have been some significant improvement on the standard belt run but it had been hung too low so the pivot was geometrically poorly behaved. Given the difficulty of holding the motor whilst setting it at a, hopefully correct, angle it was not, in practice an improvement. In my view the standard arrangement, is at best, obnoxious so it takes real talent to come up with something that isn't an improvement.

I'd start over, junk the jockey pulleys and carry the motor on a simple swivel arm affixed to the rear of the column with a pivot positioned so as to mimic the head tilt. Probably need to make able to work on either side to keep the motor out of the way. Modern motors are so much lighter and smaller than the old ones that such things are practical. Especially if you follow Michael and use a 1/4 hp one. The motor on mine was an enormous 1/2 hp thing.


john fletcher 119/12/2020 17:25:15
741 forum posts

Generally speaking it is easy to go from Star to Delta, its often shown on the back of the terminal box lid. There was a very good article on "here" a few years ago, with lots of pictures, clearly showing how to locate and bring out the extra three leads required. I'm sure a rewind shop would soon do it for you and then fit an inverter via the net for £50 or so, no need to buy an expensive one with all bells and whistles for the home workshop. John

Brian H19/12/2020 17:39:45
2239 forum posts
113 photos

Hello again Matt, I have also replied to you on your other query.


Brian H19/12/2020 17:39:46
2239 forum posts
113 photos

Hello again Matt, I have also replied to you on your other query.


not done it yet19/12/2020 18:51:57
6438 forum posts
20 photos

its often shown on the back of the terminal box lid.

It’s only shown there if the winding connections have all been brought out to the connection box - if the star point is within the motor, no delta option will be shown. It would likely be shown on the data plate as 220/440V dual voltage in that case - but that does not preclude splitting the star point and bring tails outside for delta connection.

Clive Steer19/12/2020 19:08:40
47 forum posts
4 photos

I have a Mk3 BCA with its original two speed 3 phase motor which unfortunately is specially wound and can only be operated on 440 volts.

Not having 3 phase available and also wanting the machine to have the capability of variable speed I have fitted it with a 440 volt inverter powered from the domestic mains through a 240v to 440V auto-transformer. I have fixed the motor in its low speed configuration and configured the inverter to provide 100Hz at max speed to recover the higher speeds. The original motor is quite capable and has all the necessary guards so unless it is faulty I saw no reason to change it and although the auto-transformer/VFD kit is more complicated it does transform the machine and enable less belt changing. There are VFDs available that produce 440v output from 240v but these are less common and can be much more expensive if fitted with the more capable Power Factor Correction (PFC) front booster stage.

If one doesn't want variable speed or the complication that goes with it then a static converter can provide the 440v 3 phase.


William S19/12/2020 19:55:31
68 forum posts
307 photos

Hello Matt

If it is the original 3 phase motor it should be a 2 speed, 380/400volt motor which I was told does not and will not run on a 240volt VFD. A VFD does not step-up the voltage so one would have to have a 3 phase supply to run that particular motor on a 380 volt VFD. A VFD would also limit the motor to one speed setting.

What I did was to get a 240volt single phase to 400v 3 phase converter made by Transwave. This enabled the machine to retain its original motor, which corresponds up with the speed chart.

They turn up relatively regularly on ebay, or you could buy new. They do seem to hold there value and if one acquires any other 3 phase equipment it should happily run it.

In my opinion I haven't had any call for the variable speed function the speed available from the motor and belt combinations has suited all the original tooling adequately.

I like the originality about the machine, okay the belt system may seem archaic but it does work well when set up correctly.

Just my experience, William.

John Baron19/12/2020 21:45:30
499 forum posts
189 photos

Hi Guys,

I don't know if you are aware that there are 240 volt single phase input VFD's with 380/440 three phase outputs available.


John Haine19/12/2020 22:10:49
4272 forum posts
251 photos

Hmm. If you read the overview it is slightly ambiguous. Many of these inverters can output 380V 3 ph if supplied from two phases of a 3-ph supply so the input is 380V, but of course with variable frequency. If supplied from 220V they only output 220V. This one doesn't really clearly say that it does give 380V output since one of the several input options is 380V. Over on eBay there are a lot of rather more expensive devices also from China that will only supply 380V with a 380V input.

Nigel Graham 219/12/2020 22:33:57
1772 forum posts
22 photos

Matt -

It's simple to fit a new motor to the original mounting, by interposing an adaptor:

I have just traipsed down the garden to remind myself what I did for my BCA.

I bought it from one of our regular second-hand machinery dealers, who said it came from a university who had also made the somewhat functional-looking inverter dangling from the original motor, with a plug that might have been for a 16A or 32A mains - certainly not regular 13A household type.

The dealer had nowhere in his warehouse to plug it in, so I had to buy it on sight. (I think I had been advised that would be so.) The machine itself was in good condition, despite a couple of small drill dimples in the table.

I was not prepared to risk the electrics, so contacted Newton-Tesla.

They were understandably worried about me sticking one of their nice new inverters and controllers on a motor of known type but unknown history, and equally understandably, keen to sell a nice new motor too.

I had no problems fitting the replacement motor, entailing 2 items : -

- An adaptor-plate. I used 20mm thick PVC in near-BCA Grey. You could use aluminium, or as Michael G, says above, plywood! Four clearance holes match the original mounting, and 4 tapped M8 match the smaller new motor's feet. (Use screws with their heads in counter-bores if in plywood, of course.) I turned a broad but shallow central recess from each side to stiffen the plate - possibly needlessly, but PVC is fairly flexible.

- A bush to fit the original pulley on the smaller, new spindle. The important point of course was concentricity. Plus a new key, or the original modified, to pass through the bush wall and fit its new home.

So all quite straightforwards, helped by the machine's open layout.

The tapped / counter-bored holes are necessary to set the plate flush against the pad on the column, which with the plate's thickness help put the pulley in about the right place.

John Baron20/12/2020 11:07:22
499 forum posts
189 photos
Posted by John Haine on 19/12/2020 22:10:49:

Hmm. If you read the overview it is slightly ambiguous. Many of these inverters can output 380V 3 ph if supplied from two phases of a 3-ph supply so the input is 380V, but of course with variable frequency. If supplied from 220V they only output 220V. This one doesn't really clearly say that it does give 380V output since one of the several input options is 380V. Over on eBay there are a lot of rather more expensive devices also from China that will only supply 380V with a 380V input.

Whilst that might be true for some devices it isn't in this case ! Its a straight 230 volts AC input and 380 volts three phase output. Yes there are some 380 volt three phase input 380 volt three phase output ones on there.


Matt Mackeson20/12/2020 11:42:25
10 forum posts
4 photos

Thank you all for the comprehensive replies. I don't think I have ever had such a quick and thorough set of replies to any post on any other forum!

I took the access plate off and found this handy wiring diagram for the two speed switch. If I understand this correctly the motor uses both star and delta for the two speeeds?

So it seems I have three options:

  • a new dual voltage 3ph with a VFD and adapter plate
  • a rotary phase converter
  • Look further into the VFD's posted by John. From what I understand this would give me a single speed on the current motor but then give me speed control through the vfd?

I am learning a lot about electric motors through all this so thank you all again for the help!

Matt Mackeson20/12/2020 11:45:42
10 forum posts
4 photos

Ah no I think I made an error there. Because the current motor isn't dual voltage I wouldn't have any speed control with one of the 240V to 380V vfd's. Is that correct?



Nigel Graham 220/12/2020 12:18:57
1772 forum posts
22 photos

Oops! I made a significant omission in my first reply - the guard over the motor-pulley!

The location of my jig-borer in a tight corner probably makes it less necessary but it ought still be fitted.

It was deigned to fit the original motor but I think it would be fairly easy to make for it an adaptor-plate screwed to the tapped holes provided in the face of the motor.

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