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Calling all Startrite Mercury drill owners - opinion on noise

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Graeme Durant 123/11/2020 20:33:31
27 forum posts

I have been the proud owner of a Startrite Mercury bench pillar drill for many years. And for as long as I can remember, it has been noisy! Hard to describe, but it seems to come from the spindle, and it's an intermittent kind of knocking. Maybe slightly rhythmic, coming and going over seconds. Not terrible, but annoying!

It drills accurately, and I love the feel of the sensitive feed, so no complaints about its capabilities. But I always intended to take a look at the bearings to make it run a bit quieter. Lockdown finally gave me the excuse!

I took the motor off first, and since it was a bit noisy on the bench, I replaced the bearings. One was slightly gritty, and because they are so cheap and easy to replace, I went ahead and replaced both. It's a single phase (split phase without any starting capacitor) so it's never going to be super smooth. Changing the bearings I think improved it a bit. Still hums and vibrates to the touch in use. But this wasn't what I thought was the source of the main noise. Hence on to the quill and spindle end....

I removed the quill and stripped it all down, but it seems to me at least that the bearings are all good. I exposed them all, cleaned and re-greased them, and tightened them all up again. They felt silky smooth, so as a test I then tried spinning them up at speed on my lathe. No noise at all - runout good too. Phew, because those bearings are not so cheap!

Whilst the quill was out, I also ran the drill so that the spindle pulley and its bearings were tested alone - as was the reinstalled motor. Nice and smooth and quiet. Certainly no knocking. So when I reassembled the quill onto the machine, and ran it again, I was disappointed to find the original noisiness return, unchanged.

Further experimenting suggests it's the backlash or slop in the spindle spline drive. The clue was that if you add a bit of load to the spinning chuck - gentle hand pressure - the noise ceases. And if you jam some wooden toothpicks into the spline to effectively lock it - again, no noise. So with no load applied, I think the spline is essentially rattling to and fro, making the noise.

So my question is - do they all do this? Or is my spline worn?

When stationary, you can feel the slop due to the looseness of the spline. A certain amount of looseness is I believe required so that you can actually move the quill up and down - but how much is correct? In my case, I can move the chuck about 2.5 degrees (measured as 1mm at the circumference of the chuck, if that makes sense). I should add that my spline looked unworn to me - at least the male steel part - blemish free with original machining marks intact. The bronze female part was hard to see, so that may be the culprit.

Or like I said above, do they all do this? Or maybe all the single phase ones do it, since the motors are a bit noisier, thus inducing noise into the spindle? Any thoughts or guidance most welcome!


roy entwistle23/11/2020 21:03:37
1336 forum posts


I've never noticed much noise on mine, there is a bit of play but not a lot, probably what you would expect for the quill to move up and down


Clive Foster23/11/2020 21:12:24
2625 forum posts
91 photos

This sort of thing eventually happens to every drill as splines and pulleys wear.

Have you verified that the pulleys are still properly aligned and that both belt and pulleys are still in good condition.

Small mis-alignments and uneven wear can cause surging of the drive system as the belt moves onto and off of the pulleys. Any sort of load is usually sufficient to damp the effect down and absorb variations but running light there may be just enough change to rattle against the splines. An unbalanced pulley can also be enough, unlikely in your case.

If I recall correctly the `mercury belt tensioning system isn't terribly precise when it comes to keeping the motor shaft and quill exactly perpendicular and preventing vertical shifts.

I have seen one where the pulleys and motor were so badly out of alignmnet that you could almost ssuepct sabotage. The belt was terribly torn up with black dust everywhere. It wasn't quiet.


Graeme Durant 123/11/2020 21:22:05
27 forum posts

Thanks Chaps.

Clive - I aligned the pulleys vertically using a straight edge, and the belt seems to run off them nicely - no binding visible from the side. But I have to say that the belt does oscillate in operation, on both sides but mainly the "slack" side. I have tried adding tension until it's clearly too tight - and also reducing tension, until it's too slack - but no tension I could set would fix it. The belt was new not long back, but on close examination it does have a small bump at its join, despite being a Medway brand. Or maybe because of that - I'm no belt expert!

I did also measure the runout on the pulleys - the motor one was 0.2mm, due to the grub screw fixing pushing it off centre. It sounds from what you say that any slight irregularities could be the cause of this. Would the belt oscillation count? And if so, how can I try and fix it?


Pete.23/11/2020 21:40:51
453 forum posts
60 photos

Graeme, I have one of these sitting on my garage floor with a burned out motor, waiting to be stripped down and refurbished when I have a chance.

On inspecting it, most of what you see is just sheet metal around a kinda skeletonised casting inside, is it possible some of the sheet metal body is vibrating or knocking?

Graeme Durant 123/11/2020 21:56:41
27 forum posts


It is exactly like that - and it does! But after a lot of thought and experimentation I don't think that's the problem I'm seeing. When running the motor you can definitely feel the vibration it generates being transmitted into the sheet metal. But there are two parts to the sheet metal work - the main casing, and the "brackets" that attach the motor. These are separate, and don't touch. The motor mounting part is only attached (with fibre washers) to the solid casting. The main casework is also attached to that casting, but at different places. Hence the vibration isn't transmitted into the main casework - the slight flex in the motor mounts seems to detach the motor vibration quite effectively.

But that's not to say that the vibration isn't coming through via some other route. Via the belt maybe? Or even through the casting? That's one reason I wondered if the single phase version was noisier than a three phase version?

Dunno - more questions than answers at the moment!

Martin Kyte23/11/2020 22:16:22
2309 forum posts
38 photos

Yes, that's exactly the noise they make. Seriously though I think most of the noise on mine comes from the belt cover side panels. I've never considered it an issue, it drills fine. It's a little fast for larger drills and annoyingly the chuck on mine will not close down on a 1/16 drill but apart from that it's a perfectly servicable general purpose bench drill.

regards Martin

Clive Foster23/11/2020 22:27:44
2625 forum posts
91 photos


Belt oscillation suggests the drive is surging. Anybodys' guess whether that is a reaction to another issue or the cause.

No idea as to how it could be fixed if everything is set up right. I usually find such problems go away when you start over and build things up carefully with known good components. Frustrating not to know what teh probelem actually was but fixed is fixed.

I have seen such oscillation/surge issues when a belt has a bump in it. But that was a made to order one maybe 15 ft long and the natural elasticity of the belt semed ot dampen things well enough. But the effect of the bump was quite visible.


Pete.23/11/2020 22:34:33
453 forum posts
60 photos

I guess it's a case of, how much does it annoy you, how far are you willing to go to stop it, as you posted here, it's probably annoying you sufficiently.

Put a largish drill bit in, clamp a thick piece of steel in a well bolted down vice, while running and making the noise, put firm constant pressure into drilling what's clamped in vice, if something is loose in between the motor and the chuck, constant tension should lesson any noise, listen and see if this makes much difference.

If not, take all the sheet metal covers off and run it, these are the first things I'd try.

Graeme Durant 123/11/2020 22:49:18
27 forum posts

I guess it does annoy me! But if someone told me "they all do that guv" then I'd forget it and move on. As has been stated - and Martin confirmed this for his - it drills well and works perfectly. But since it's in bits on my bench right now, it feels like the time to address it - now or never. And in some ways, understanding the problem is a part of the fun. Isn't it?!

So here's a question - how "smooth" is the drive from my single phase motor? It's casing vibrates quite a lot to the touch, but is the actual rotation "noisy" due to the imperfections of the split phase style motor? I have felt some of my other motors around the workshop, and this has loads more vibration associated with it. Compared to Cap start and 3-phase via a VFD. It is the only split phase motor I have.

And if it were considered noise in the rotation, could this induce the surges that Clive talks about - and hence my belt oscillations? I think those belt oscillations do coincide with the noises in the splines, as the effective speed of the drive changes, and shunts the splines back and forth. So finding the source of the oscillations could be the key here.

Or am I on the wrong track?

Pete.23/11/2020 23:13:43
453 forum posts
60 photos

Just to clarify, the main concern was a mechanical knocking noise coming from the spindle area?

Graeme Durant 123/11/2020 23:16:09
27 forum posts

Yes - which seems to be coming form the spline - since jamming this kills it completely....

Pete.23/11/2020 23:33:49
453 forum posts
60 photos

Apologies, I read your first comment very quickly and didn't take in what you said about the toothpick, so the noise is gone with a toothpick in the splines?

Graeme Durant 123/11/2020 23:53:24
27 forum posts

It is. If you lock up the splines, the noise disappears. So from what's been said so far, it sounds like either;

1). The splines are worn, so making more noise then they should - and AFAIK there's no easy fix for that beyond replacing them - which is scarily expensive. I'd live with the noise in that case.


2). The spines are OK, and it is the drive that is surging. I guess I read that as varying in speed, sporadically for some unknown reason. From what Clive said, it could be due to many things, and may never be determined. Hence my question about the motor itself, since it does seem to be prone to vibration.

Just been thinking about this whilst out for a late night bit of fresh air. I have a similarly dimensioned cap start motor kicking around, and might see if I can temporarily replace the original, in case it alters the behaviour. All data here is useful after all. Won't be able to do that until tomorrow, but unless any better ideas surface in the meantime, I think that'll be my next experiment....

Pete.23/11/2020 23:53:46
453 forum posts
60 photos

If the noise is gone with toothpick wedged in there, then that's your problem, I haven't looked in mine to see exactly what's going on with the spindle, but if it's the bronze female part you think is worn, what you could possibly do, is make a female spline from some 3mm brass that fits the male part with no slop, and attach it to the top of the female part like a thick splined washer.

I haven't looked inside mine, so not sure how it could be fixed to the female part, but if fitted so the male spline engages on the front face at full length , with the splined washer stopping it from spinning back and knocking when not under load.

Graeme Durant 123/11/2020 23:57:53
27 forum posts

Mmmm, interesting idea. I guess the drive is always in one direction, so the "tight" spline would only be taking up that unloaded rattle. Maybe option 1 in my ist isn't a case of just giving up after all....

I will try the spare motor though, as it's easy to do. May have no effect, and then that starts to narrow the answer at least!

Graeme Durant 124/11/2020 00:01:41
27 forum posts

Pete - next time you pass your garage, maybe you could grab the chuck on your dead drill and just see how much play is in the splines? Just as another data point? As I said, the body of my chuck moved about 1mm against the stationary shaft. I have no idea if that is "normal" or "badly worn", for the Mercury, hence all input is valuable!

Pete.24/11/2020 00:05:54
453 forum posts
60 photos

I'll go and check now!

Pete.24/11/2020 00:24:45
453 forum posts
60 photos

Holding the front pulley with one hand, I'd say 1mm of movement at the chuck seems about what I have.

Graeme Durant 124/11/2020 01:41:52
27 forum posts

Thanks Pete! That is a useful data point. It either suggests mine isn't too far out of spec - or your machine has similar wear. But I'd favour the first!

Let's hope my experiments with changing the motor yield further evidence tomorrow....

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