Member postings for James G 1

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

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.

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.

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.

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.

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

Hi Clive,

Thanks for your comprehensive reply - it's amazing how subtle can be the details of a simple mechanism. Certainly as you say consistent lubrication should help - the latest version as discusssed on this thread is enclosed and may effectively have it's own oil bath. Hopefully I'll be able to build it and enjoy the luxury of using it.

Thanks again,

J.

Just to say that I am also following this with interest and would be interested in drawings if available.

Is there any advantage in having matching slight tapers on the engaging surfaces of the dog clutch i.e. on the drive dog and the semi-circular end of the recess with which it engages ? The taper would be such as to have the dog more narrow at it's end than at it's base, such that there would be a slight tendency (depending on taper angle) for the clutch to disengage unless held by a detent.

The only dog clutch I have had a chance to examine was a multi-tooth clutch in the feed gearbox of a toolroom type mill and this had a very definite taper on the dog faces, hence my enquiry.

J.

To follow up on the previous excellent description, the most straightforward arrangement is to have the dog clutch turning at spindle speed.

I believe that the shaft where the dog clutch is located must not be running any faster than spindle speed, as this allows for re-engagement at incorrect relative positions.

In the general case, a dog clutch located on a shaft which is running more slowly than the spindle will not work correctly either. This is why a clutch located on the leadscrew will not suffice.

However, if the shaft with the dog clutch is rotating more slowly than the spindle by a ratio of 1/N, where N is a whole number, then I think it will work. e.g. if the dog clutch shaft turns at 1/3 of spindle speed then all will be well. However dog clutch running at say 2/5 of spindle speed will not work.

The above is my understanding from reading - particularly Martin Cleeve's excellent book.

The Boxford 280 and similar lathes have a built-in reduction in speed of 1/3 from spindle to the first accessible shaft of the feed train, hence my interest in the niceties!

That looks great! I would be most interested in any and all details of this mechanism. I have been scratching my head trying to figure a way of doing this internally to the headstock using a dog clutch on the feed and feed reverse gears. This looks like a very neat solution. I think it will apply to other lathes in this series as well such as the 280.