QDM750/Kerry Super 8 spindle bearings

[James G 1Participant @jamesg1]

Hi All,

I am doing a tidy up of a drill press – a Qualters and Smith QDM 750 (backgeared, very similar to the Mk2 Kerry Super 8). There was noticeable play in the top spindle bearing. I have pressed out the bearings and am pondering re-assembly with replacements.

The bearing arrangement doesn't seem to provide for any way to control the preload on the bearings or even to ensure that the angular contact bearing at the top is actually taking the axial load. The inner and outer races of both bearings are press fits, with the outer race of the top bearing probably the least tight fit. I have included a (very) rough sketch below.

Any thoughts on how this was meant to go together would be appreciated.

Regards,

James

[James G 1Participant @jamesg1]

[Oily RagParticipant @oilyrag]

James,

I also have a QDM750 which was gifted to me some years ago (because it had stood outside a famous (now defunct) car factory for many years and had been considered scrap). I rebuilt it and from memory the DGB bottom bearing acts as the locator for the spindle whilst the AC top bearing takes the axial load when drilling. The bearings which came out of mine were totally shot after being weathered and after cleaning up the spindle, the fit into the inner race of the top bearing was less than I would have preferred, Loctite bearing fit coming to the rescue – but it has all worked well enough. Which bearings did you fit as there was a late model change from the earlier bearings which, I believe, was a change to the tolerance class? Never seen anything definitive on this but was told this by a reputable M/C Tool rebuilder.

Have you managed to find an operators manual for it? The Tony site only provides the advertising literature as seen in the write up on the QDM range of drills.

Lovely bit of kit by the way.

Regards,

Martin

[James G 1Participant @jamesg1]

Hi Martin!

Thanks for your reply.

I've yet to order up some bearings. The AC one is marked 7302B and the DGB one is 1 x 2 1/4 x 5/8.

My thinking currently is to fit the AC bearing to shaft and housing, and then press in the lower bearing (supporting inner and outer races of both bearings evenly).

I guess what I'm wary of is that there will be some room for the outer race of the AC bearing to slip upward under drilling forces until it takes up any small clearance between the bearing and upper circlip. This would leave the AC bearing relatively loose and would leave the DGB carrying the axial as well as radial load ?

Maybe I'm overthinking it, although it would account for the slop I saw that convinced me to press out the bearings.

J.

[Oily RagParticipant @oilyrag]

James,

Sorry for the delay in responding.

I have now had a chance to dig my workshop notes out on this rebuild – unfortunately I no longer have any photographs (the curse of mobile phones that get broken, lost, or stolen!) but from my notes I measured the distance between the bearing shoulders of the spindle quill and also the depth of the retaining circlips, the upper (AC bearing) clip gave a +0.004" clearance on bearing outer race width. I did consider packing this but eventually settled for 'as it was' condition.

The way I see it the AC bearing supports the mandrel and the lower DGB 'floats' to accommodate the upper bearing. I used a Hoffman RLS8-V3 DGB and a SKF 7302 BEP AC. With it all assembled the end float was zero – I believe the end float you have experienced may have been caused by the AC bearing wearing through lack of lube, this will introduce end float. I would certainly recommend you check the gap between the top retaining circlip and bearing to ensure a close fit. A spring 'wobble' washer could be used if it is excessive. Also worth replacing the circlip if it is damaged in any way.

Let us know how you get on.

Have you any response about a manual?

Martin

PS – my method of assembly was to press in the AC top bearing into the quill, then supporting the inner race of the AC press in the mandrel which had the DGB bearing pre-fitted to the quill shoulder dimension, when the DGB outer race was ready to go into its housing I tapped it in gently as the mandrel was still under load. The upper bearing was as I said in the earlier post an 'easy' fit due to the corrosion from being in the elements. The drill has been fine with a very quiet spindle and no overheating.

Edit for PS

Edited By Oily Rag on 19/08/2021 18:31:05

[old martParticipant @oldmart]

It does look strange but being a drill, there should be none of the sideways forces associated with a milling machine spindle.

[James G 1Participant @jamesg1]

Much work later.. more knowledge but not entirely happy.

First off, there is very close to 1mm of extra depth in the top housing over and above what is required to take the bearing and metal dust cover. I have a washer made up to take up this gap. I think it is a fraction too tight at 1mm for the snap ring to fit perfectly so I may thin it/re-make it .

I then fitted a set of bearings (import 'Zen' branded). With the slop taken out of the top bearing, the lower bearing was running unpleasantly hot at the top speed. The top bearing was fine temperature wise. Cue another disassembly and the loss of the newly fitted bearings.

The disassembly threw up another nasty – I went to drive out the bearings from the top down. The inner race of the AC bearing pushed out of the outer race, but it brought the balls and cage with it. The balls then started to impact on the shoulder below the bearing. I stopped once I saw what was happening and ended up driving the bearings out from the bottom. The balls had raised a couple of dings on the shoulder which I dressed out. I had used the technique of driving out from the top when I originally dis-assembled it, and on that occasion, the inner race of the AC had moved down, leaving the balls in the outer race where they could do no harm. So it seems like it might be the luck of the draw.

[James G 1Participant @jamesg1]

The lower bearing was sitting on a shaft which I measured at about 0.015 to 0.017mm (say 6 tenths of an inch) oversize. Then, the outer housing is also an interference fit which I reckon all makes the assembly process more demanding and is probably significantly reducing the clearance in the lower bearing.

I took the shaft down to 1 or 2 tenths oversize (by hand with 400 grit paper). It actually went marginally under in one spot but overall should still grip well I think. I also gave a minute or two smoothing the housing surface for the lower bearing – I don't have tools to measure the bore but it was still certainly an interference fit.

Then I fitted new bearings. I applied a slight pre-load by lightly tapping in the outer ring of the lower bearing as a last step. This definitely takes the slop out of the upper bearing. There was certainly a temperature rise in the lower bearing but more acceptable.

The next problem though was the appearance of a new noise from the pulley/spindle interface. I suspect that either a) wear b) misalignment or c) a slight bend in the spindle was being 'tolerated' by the slop in the top bearing.

At that point fate intervened and the spindle slipped and dropped square on the table. This shifted the lower bearing slightly downward I reckon. Cue return of some slop in the top bearing.

Around this point I fitted it all together and for now have cut my losses.

It's all certainly running more quietly and smoothly than before. Some day maybe I'll go back to it.

[Pete.Participant @pete-2]

What kind of press were you using to install these bearings? An arbor press gives much better feedback than hydraulic for bearing installation.

[Pete.Participant @pete-2]

The people who designed, machined, and assembled these machines knew far more than you or I about them, I don't think removing material from any of the parts is a good idea.

[Pete.Participant @pete-2]

I actually have mk2 qdm750 on my workbench that is about to have a full strip down rebuild etc, it is on the urgent to do list, but probably won't happen for maybe 4 weeks, I will do a full photo logged rebuild so other owners can reference it, maybe offer their experience during my rebuild.

[James G 1Participant @jamesg1]

Hi Pete,

Best of luck with the rebuild – I'll keep an eye out for it in due course.

I used a hammer (carefully) to fit the bearings along with suitable drivers to prevent loading the races. I rested the assembly on a piece of softwood. As you say an arbor press would be ideal.

Regards,

J.

[Oily RagParticipant @oilyrag]

James,

I missed the back end of this thread whilst away on holiday. I see you had just under a 1mm clearance between the top AC bearing and the underside of the circlip. Is this possibly down to the 'Zen' (never heard of these before! ) bearing being undersize in assembled width?

When I was replacing my bearings I searched around for known makes – I was offered 'Charlie' bearings for around £8 to £10 each, but genuine Hoffman, FAG, or similar were priced around £60 to £70 each! This was from a well known bearing supplier based in Norwich. I then tried two local suppliers of Vintage bearings who both offered known makes for all 4 spindle and pulley assembly bearings for a total of £55 (and threw in new circlips for the price ).

Just for reference for other QDM 750 owners the pulley assembly bearings are:- Top bearing EE9 or KNLJ1 (1" x 2" x 3/8" ) and the lower bearing is a Hoffman LS25N or equivalent (25mm x 52mm x 9.3mm ). These are both narrow light journal open ball races of 3/8" width.

I have now decided that I ought to finish the re-build by re-painting the machine and have been trying to match the original Hammerite hammered finish paint which appears to be a deep blue/charcoal grey colour. I suspect this was specially made for Q&S as I have so far had no luck sourcing any suitable paint from Hammerite. Has any one tried mixing Hammerite – I suspect I might need to mix Black and Light Blue to get a suitable shade. The belt guard also seems to be an 'Aluminium' hammer finish as opposed to the Hammerite Silver. I think this calls for a touch of black mixing with silver to get the desired colour.

Anyone have any experience of mixing Hammered paints?

Martin

[Dave HalfordParticipant @davehalford22513]

Don't mix older an new paints, the base formula is different.

[Oily RagParticipant @oilyrag]

Dave,

I had heard that it is a no-no to mix Hammerite paints as they will not mix colour wise (giving a scattered and streaked colour to the paint finish); I expect that someone has done this with an old tin and a new tin, Presumably fresh pain may mix though? I'll try some light blue mixed with Japlac black and see what that does – it is what I currently have and they are both of a similar age.

James,

Re-reading your earlier post it struck me that the alignment issue of the lower pulley bearing, which is held in a floating steel pressed cup, could be an issue. I realised the steel cup which holds the lower pulley bearing needed slackening off to allow the puller assembly to find it's own seating. In my notes on the re-build I had quite a job to get the spindle assembly to line up – and the overarm was not bolting down snugly: I had left the dowel pins in and tried fitting them in place, in the overarm, as I bolted the overarm back to the head casting – with the lower bearing plate loosened off I took the dowels out and bolted the overarm down lightly before lightly driving the dowel pins in from the top. This cured all the binding. There is a definite procedure to the build with these machines!

Another point to beware of is the bull gear detent pin can become locked if the latching plate overshoots whilst assembling the spindle pulley assembly prior to the bearings being pressed on.

Martin

[James G 1Participant @jamesg1]

Hi Martin,

Your point regarding the lower pulley bearing is well made.

I let the lower pulley bearing find it's own best alignment by removing the belt tension and gradually nipping up the mounting bolts, all the while rotating the spindle by hand to allow it to nudge the pulley into alignment. This is definitely a necessary step as you say.

I'm happy now with the pulley setup. The spindle bearings are noisy though. It may as I mentioned be the quality of the bearings themselves or my handling of them. If you could send me on the details of your bearing supplier it would be appreciated.

Regards and thanks,

James

[Mike PooleParticipant @mikepoole82104]

Zen are a German company who manufacture bearings in China. If the bearings meet the German standards they claim to then the bearings could well be of adequate quality and well priced. Buying the most expensive bearings could be a mistake as could be buying the very cheapest but for different reasons, the most expensive could exceed what is required which will do no harm except to your wallet, the very cheapest could be next to useless which also harms the wallet as better quality will need to be bought again.

Mike

Edited By Mike Poole on 02/10/2021 10:48:02

[Oily RagParticipant @oilyrag]

James:-

I have sent you a PM

Mike:-

My experience of JV companies in China is that they are totally influenced by the Chinese management, this applies to German companies as to all other foreign investors in Joint Venture organisations. I dealt with a famous German piston manufacturer with a Chinese JV and even though it carried the German trademark they had very little input to 'failure determination' as the German parent company charged high fees for their skills (the only way to extract money for the parent company ). We had catastrophic piston failures which I was responsible for determining the causes. I was the fifth engineer to visit the China JV in Qingdao to review their process and procedures. I surprised the 'Kwality' team there by asking to see the raw stock delivered in to them (no one preceding me had done this – just looking at the casting process ). I had had a piston examined by a metallurgist who was ex AWQA and was a consultant to one of the top piston manufacturers in the UK. His report highlighted areas of entrapped dross, small ferrous inclusions (namely steel swarf and carbide chips ) but interestingly undissolved balls of copper within the metallic structure. This indicated poor quality feedstock in the process and a melt furnace with insufficient heat to fully dissolve the copper seedings needed to correctly alloy the piston.

The raw material I found to be abysmal – the last stillages off a delivery were covered with sacking and underneath were ingots of total dross (literally ). Then I turned to the furnace melt temperature records and after some time the Chinese eventually found a page for me from a date I had requested giving the 24 hour temperature monitoring data. The hand written notes struck me as falsified, I asked how much they paid the inspector, when they asked why I asked that I pointed out the same person had written the sheet for the whole 24 hour period in the same pen!

So, my take on this is that anything made by a reputable Western company in China has little bearing (no pun ) on the quality of the product!

Whilst agreeing that payment for items needs to be reasonable for an expected quality product – I found bearings which were within my expectations for reputation at a wholly reasonable cost. £60 – £70 pounds for a new old stock bearing is excessive! £13 odd on average for 4 bearings is liveable with. A drill is after all a semi precision tool.

Martin

[Pete.Participant @pete-2]

Hi James, I've just taken delivery of a new motor and inverter to start this little project, but while rearranging the workshop I was moving my toolbox/workbench and all the wheel castors collapsed as I cheaped out on them while building it, I'm just in the process of repairing it and should be able to start the Qdm750 in about a week or so, just letting you know I hadn't forgotten.

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