Centec 2B – New arrival and Q&A

[Dave HalfordParticipant @davehalford22513]

That noise may even be a crack working already as the motor wobbles it sounds a bit like metal scraping past metal. Cutting the hole for the motor has weakened the cabinet backplate so much it needs some extra top to bottom bracing anyway.

Check the pulley ,then the shaft, the previous owner has done something he shouldn't.

[William AyerstParticipant @williamayerst55662]

No cracks, got the motor out and gave it a run with and without power – there's a faint scratching as it rotates – I'm not sure if this is the same as the rhythmic sound it gives out when the belt is connected – it seems to be once per revolution and I think that'd probably come out as a shriek or whirr at normal RPM?

Either way, here's the video:

https://www.youtube.com/watch?v=X8XryY7FD7Q

I've not the faintest on how I might go about doing anything about this, is it best left to a specialist or is there something obvious I can check?

The motor baseplate was 'skewed' on the L-brackets with relation to the axis of the motor and pulleys.

Edited By William Ayerst on 05/08/2021 16:11:13

[William AyerstParticipant @williamayerst55662]

An example of the original knocking/tapping sound with the mill in use is in this video – timestamp from 0:23

[Dave HalfordParticipant @davehalford22513]

The pulley wobbles Will, and it sounds like a shot bearing as well.

You need to get that pulley off and see if the shaft wobbles. If it does it still may just be the bearing

The scraping sound might be the armature touching inside if the bearing is really bad.

Or you just buy a new motor, a 'specialist' will cost you 3 times what a a new motor will.

Edited By Dave Halford on 05/08/2021 16:51:32

[William AyerstParticipant @williamayerst55662]

OK! One step at a time, then!

I guess a gear puller to get the pulley off? Something like these? https://www.amazon.co.uk/Puller-Bearing-Removal-Internal-External/dp/B01CIEUXQQ/ ?

[Dave HalfordParticipant @davehalford22513]

Undo the grubscrew it may not be on very tight. Or rather it should not be a tight fit.

[William AyerstParticipant @williamayerst55662]

Right you are – it slid right off. Motor axle is straight as an arrow – less than a thou out at the tip by my dial indicator. The pulley is 3/4" bore, with two vee grooves – minor dia 1-5/16", major dia 2-5/16". It looks like it has been bored, or the factor finish wasn't great. The axle has some score marks on it near the key.

I reattached the pulley and it was wobbly again.

I guess this means the noise in the motor may be the bearing, but it's not gone enough to affect the play of the axle?

Is it safe to rest the motor on the chip tray / etc. with a belt on it to see if the knocking/tapping is reduced/removed ? That might tell me if the sound is coming from the motor mounting arrangement?

[Richard MillingtonParticipant @richardmillington63972]

If the pulley is "wobbly" it is probably not bored correctly, do you have a lathe you could clock it in? If the motor bearings are rough you should be able to tell by rotating the spindle by hand, does the spindle move when you pull it to the side. How does your motor mount? Is the adjuster loose? Does it have pivots, are they loose?

[JasonBModerator @jasonb]

Once you get the wobble sorted out mount those cutters the other way round and feed the work in from the left to the right. That way the cutting force will cause the nut to tighten up rather than keep coming undone as it is in your video.

[Dave HalfordParticipant @davehalford22513]

Posted by William Ayerst on 05/08/2021 20:18:36:

Right you are – it slid right off. Motor axle is straight as an arrow – less than a thou out at the tip by my dial indicator. The pulley is 3/4" bore, with two vee grooves – minor dia 1-5/16", major dia 2-5/16". It looks like it has been bored, or the factor finish wasn't great. The axle has some score marks on it near the key.

I reattached the pulley and it was wobbly again.

I guess this means the noise in the motor may be the bearing, but it's not gone enough to affect the play of the axle?

Is it safe to rest the motor on the chip tray / etc. with a belt on it to see if the knocking/tapping is reduced/removed ? That might tell me if the sound is coming from the motor mounting arrangement?

This perhaps / maybe lark is fun isn't it.

You either buy a new pulley or bore it out properly and sleeve.

If the motor shaft feels smooth it may have just swallowed some swarf. You can carefully take the back plate off the motor, don't loose any spacers, then the front. If the bearings are ball races & fully sealed it's hard to tell damage. if they are loose metal plates or half seals wash the grease out and spin them, a bad one will catch and dry they are quite noisy.

I should add check the armature for rub marks.

Edited By Dave Halford on 05/08/2021 20:59:25

[William AyerstParticipant @williamayerst55662]

I did a quick check before turning in for the night – the pulley is about 5 thou out at the bottom of the grooves and 20 thou out at the tops (and at least one end). There is about 5-10 thou slop in the fit on the motor axle which I guess is where that's coming from? I can clock up the pulley in the lathe – but maybe more straight forward to shim it opposite the grub screw?

Either way I'm not sure how 1/2mm of misalignment could cause the sounds that I was hearing tbh?

Next plan is to see if I can get the belt hooked up while the motor is off the mounts but otherwise stable, to see if that was where the 'big noise was coming from, and then to get inside to look at the bearings (what to flush/regrease with, if open?).

[duncan webster 1Participant @duncanwebster1]

Is the motor mounting just a bit of bent plate fastened to the back of the pedestal? As someone else said, it all looks too flexible.

[not done it yetParticipant @notdoneityet]

In addition to JB, only fully tighten or loosen the arbor nut when the arbor support is on and secure. Just good practice. The Clarkson spanner needs to rest with the Clarkson holder.🙂

Edited By not done it yet on 05/08/2021 22:58:05

[JasonBModerator @jasonb]

With the motor being thrown about so much due to something like the pully being so out of true then the noise could be coming from almost anywhere. There is no movement on any of the motors on my mills (3) or lathes (2), Stop that and then look deeper into the motor if there is still noise. Is it on rubber mounts that have perished?

For those that did not follow the link here is the motor movement at 56secs in, Maybe this is why those that like old iron suggest bolting it down to the floor

I would forget about trying to shim opposite the grub screw. machine a plug, set pulley up in the 4-jaw to run true then bore out to suit the plug and loctite it into place. Without removing pully from chuck bore the plug to a close fit on the motor shaft using the shaft as a plug gauge, re-drill grub screw hole and tap and see if that helps. Also check motor shaft ha snot been worn by the loose pulley and also check old belts have not become stiff and taken on the set of where they fit.

I lead to believe this is one of the joys of owning older second hand machines

[William AyerstParticipant @williamayerst55662]

Looks like the smaller belts are OK, but the longer from the motor to the spindle has a very slight set in it at one point. I could always get the second belt for the motor and replace both at the same time? The spec on the belt is "PIX X'tra AX 71 / X 13×1800 Li" – should I look to replace like for like? It seems fairly new…

This is what the motor mount looks like – bent angle and thick plate. There is more angle on the inside of the base that these are connected to – you can see the far one inside the hole:

I hooked up the motor belt while it was outboard of the stand. I appreciate there's nowhere near the same amount of torque being applied since its just its own weight holding the belt to tension, but there's not even a whisper from that end:

So, what's the best solution for this? I wonder if a cage or frame made out of angle that can bolt to the back of the mill but also rest/be bolted onto the plinth might work, rather than having it suspended in air? Potentially polyurethane bushes or something to stop vibration?

not done it yet – got myself a clarkson spanner and a 1" spanner to lock the spindle and sort the nut – much better!

[not done it yetParticipant @notdoneityet]

Don’t even try to get a belt matching a used one – rarely does it work. Pulleys need to be aligned, so matched pairs are a necessity.

I remember one belt drive that had at least half a dozen drive belts and one belt was doing nothing – it might just as well have not been fitted!

Wait until you decide what to do with your motor/pulley/ fixing arrangement before ordering anything. My local ABC will supply me with a couple of sizes for me to choose the better option. The unused belt(s) are returned – as long as they have not been run.

Belts have enough ‘spring’ in them so the motor should be bolted down solid.

Is your vertical head driven by two belts?

Edited: Grease that motor!

Edited By not done it yet on 06/08/2021 11:41:42

[Dave HalfordParticipant @davehalford22513]

If you bolt to the wood the motor might drum.

The angle looks like the legs from a bath, 3mm braced across the ends would be better (like two triangles) and will transfer the load into the base + extra bolts with heavier washers to clamp to the stand .

[duncan webster 1Participant @duncanwebster1]

Mine has a pair of goalposts made of angle inside the pedestal. The uprights are bolted to the sides and the motor sits on the crossbars. This is a truly awful set up, the only way of adjusting the belt is with a jack underneath, slotted holes in angle uprights. This entails lying floor on your back with your head inside the box. Thankfully I've never had to adjust the belt since fitting it. It's only plus point is that it is good and rigid

[not done it yetParticipant @notdoneityet]

JB wrote: I lead to believe this is one of the joys of owning older second hand machines

But worth it once sorted, with both a vertical and a horizontal miller in the one very good hobby machine.🙂🙂

[William AyerstParticipant @williamayerst55662]

I know this is going to sound stupid, but I've never taken a motor apart, nor inspected or greased a bearing before Where should I start?

Dave – The angle doesn't reach all the way to the base of the machine, but I see what you mean – a pair of right angle triangles with the hypotenuse as a support for the outside? This is what the setup looks like in diagonal form 'as is', I have added a light green line to represent the diagonal support. The outside pink L-supports are slotted, as is the motor plate to the support. The inside L-supports seem to only be acting as oversized washers to the outside supports, they don't support anything.

Is it enough to have the braces reaching down to the bottom of the existing outside angle, or should I replace the whole thing? I don't know how to weld so would probably be dealing with bolted steel angle for the brace, or asking a friend or relative to weld me up an entirely new piece.

Getting inside the base to unscrew the mounting plate bolts was hard enough with nothing else in there – I can't imagine how much of a pain it would be, with the motor inside!

[Dave HalfordParticipant @davehalford22513]

It's not stupid, but you may not need to touch it, depending on how the pulley fix and mounting plate mod turn out. The brace is correct

I would put a horizontal brace right across the full width of the back and tap it some convenient size (to save too much messing inside the stand) one at each end and two to pick up the outside angle. The bottom of your outside angle also needs bolting as close to the bottom of the stand as you can sensibly get. You will need to slot the outside angle for these or use them to lock the adjustment without the slot.

That should stop the flexing

[William AyerstParticipant @williamayerst55662]

Right, so a brace across the full width of the inside-back, binding the corners of the stand to each other, and to the top of the outside angles? What material should I be looking at for this?

The bottom of the existing outside angle is about 2-3" from the bottom.

Edited By William Ayerst on 06/08/2021 18:08:02

[T.BParticipant @t-b-2]

I must admit I've not read the whole thread , but all the Centec 2B's i've ever seen have the motor mounted on a hinged platform inside the cabinet.

Its a pain to set up and the same as someone else mentioned, I ended up lying on the floor on my back with my head in the cabinet to set it all up , but the drip trays big enough as it is and takes up enough room without having the motor sticking out the back as well !

[not done it yetParticipant @notdoneityet]

… all the Centec 2B's i've ever seen have the motor mounted on a hinged platform inside the cabinet…

Mine has been mounted on a very sturdy bench since I got it.

The original single phase motor was mounted on angle iron(s) bolted to the sides of the stand, like Duncan described.

The only way to move the stand into position was to cut it in half. I bolted on eleven (I think) pairs of ~30mm wide pairs of brackets around the stand then cut it in two with a jigsaw. The two halves bolted back together are now in position awaiting a suitable juncture to shift the mill onto its base (about a metre with a 180 degree turn). When I move it, it will take some time and effort!

[John Paton 1Participant @johnpaton1]

My 2B (As well as the one I had previously) both had the motor mounted inside the cabinet on 'goalposts' as others describe. Slots in the angle give the required scope for adjustment.

The only reason I can see for mounting the motor the other way round would be to increase storage space inside the cabinet, but I would have thought that little is to be gained by that (not easy to reach into the rear part of the cabinet under the drip tray) and it must result in the machine standing well forward of other machinery / workbench.

The Centec 'goalpost' gives a very rigid mounting and belts provide ample resilience. The suds tank lies blow the removable plate below the motor mount. If not using that tank one can fill the void with sand to damp down any vibration.

Centec design always struck me as being pretty well sorted, a very capable machine for its size and as time goes on it is amazing how many continue to give faithful service.

Edited By John Paton 1 on 06/08/2021 21:50:01

Edited By John Paton 1 on 06/08/2021 21:52:25

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