Thread: Toolpost Grinder - Safe for the lathe?

Gents,

I've just finished building a toolpost grinder (pictures attached) as a bit of a project for the lathe, but I read everywhere that they can be very bad for the lathe bed an sliding parts.

Does anyone here have opinions on this, and maybe suggest possible methods to minimise problems?
I don't intend to use this much at all, maybe only for hardened workpieces.

Pictures show the flat belt (from an old upright vacuum cleaner), 75W single phase 2750RPM motor from a boiler blower, built up spindle with re-tasked ball bearings (seems to run smoothly), 60 grit 80mm dia grinding wheel, pulleys sized to give 6000RPM at wheel, and a test piece (high-carbon steel) to check operation and surface finish.

Belt guard and wheel guard still to be made.

Andrew.

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I think provided you are sensible about it and protect the ways when in use I cannot see any long term problems..

The grinding dust I believe is very bad for the lathe & I think that would be what people are referring to. I would suggest putting a thick sheet of rubber over the bed and covering as much under the chuck & work piece through to the cross slide.

The you can catch as much of the abrasive etc that comes off.

Great job Andrew!

I have a little Dumore 44 TPG. I have had problems achieving a chatter free finish which have led to a disinclination to keep fooling around with the grinder.

When I did use the grinder I found that the grit arising from dressing the wheel was worse than the grit resulting from actual grinding. I covered my lathe, a nook and cranny ridden 9 inch Hercus, with a couple of plastic drop sheets and placed a tray on the bed under the workpiece to cope with the hot sparks. Proved to be an extremely awkward setup. The grit is pervading stuff. I dismantled and cleaned the saddle after each attempt at grinding.

I have toyed with the idea of remote motor driven grinding spindle, belt drive via a countershaft similar in fashion to the grinding setup used by say, Schaublin on their 70 and 102 lathes. I found that with the Dumore access to the workpiece was restricted. The motor tends to be a hindrance.

The Dumore can run up to 38,000 rpm for internal grinding but the vibration causes auto advancement of the compound slide, another reason why the TPG resides in its tin box.

Bob.

TPG are quite safe to use provided you cover up the wearing surfaces of the lathe well and wipe/vacum everything down well after, and totally re-oil.

I always use toilet paper to wipe down with as it will catch and collect grit extremely well. Plus you save on rags.

I've used my Waldown grinder as long as I've had the lathe and it hasn't destroyed the lathe or any of the other similar nonsense you read at times.

For cross lathe grinding you must have a lock on the cross slide as Bob found out. It's absolutely necessary to get a good finish. As there is such little load on the cross slide it will tend to float in and out otherwise on the backlash. Easy to fit. When cutting you must lock the carriage instead.

Also dress the stone accurately when you change over.

I use old rags and towels to cover the lathe and wet them where the sparks are going. For heavy grinding I often put a small metal plate where the sparks fall on the rag to deflect them away from the lathe and stop burning a hole in the rag.

Don't use plastic as suggested as the sparks will go straight through it and it's also hard to wrap it around stuff to cover properly.

TPGs are excellent if used correctly.

You should make up some mounting plates to allow use of thin friction discs on the TPG, as they allow you to cut hard shafts, grind into corners, profile, grind cutters, and a multitude of other uses.

Wide stones are OK for plain work on shafts, but that's only one small realm of use of a TPG.

Nice job.

Bob if the Dumore is vibrating you've got a stone or something out of balance or off centre. The Dumor is similar to my Waldown, and I have no vibration issue ever with that.

Cheers

Rob

Originally Posted by nearnexus

Bob if the Dumore is vibrating you've got a stone or something out of balance or off centre. The Dumor is similar to my Waldown, and I have no vibration issue ever with that.

Cheers

Rob

Hi Rob,

The topic of vibration received a hammering a while back -

http://www.woodworkforums.com/f65/to...2/#post1360874

I sort of gave up....

I used plastic, which was a pain in the a..se, because I've seen what happens when a rag meets a lead screw.

I do have a beater Hercus T and C grinder that if repaired would far better deal with any simple grinding tasks. It is finding the desire and energy to fix the thing that is my problem.

Bob.

Originally Posted by Anorak Bob

Hi Rob,

The topic of vibration received a hammering a while back -

http://www.woodworkforums.com/f65/to...2/#post1360874

I used plastic, which was a pain in the a..se, because I've seen what happens when a rag meets a lead screw.

Bob.

Ummmm, I see why you used the plastic.

I have metal leadscrew covers and that's a MAJOR plus for grinding operations, so I can see now why you're a bit nervous about it now.

i'd hate to see what grinding grit does to the half nuts. Also I should mention that the chuck has to be dismantled and cleaned each time as well as that cops a big dose of dust and can't be protected.

All issues that can be overcome and the benefits are there.

eg. if you machine something with a fly cutter, you will always get machine marks, particularly with an interrupted cut. A TPG will take those completely out of the surface and give a near mirror finish. Once again you can't do this with a basic wide flat stone, you have to face it at an angle to run across the work in the chuck jaws (face it).

Bob I had a read through that previous discussion.

The vibration is obviously of concern (there shouldn't be any, particularly with small stones) and the cross slide should definitely be locked for the grinding in the photo's. I made up a solid cross slide mount for mine as well.

Harmonics and poor dressing are the issues you have to avoid and the main cause of a pattern. The grade of stone has no bearing on patterning. It is caused by an imbalance, irregularity, movement, or gear cogging.

I couldn't see the pattern in the photos. For absolutely mirror finish you will probably need to grind wet, which is beyond home workshop use.


Cheers

Rob

Well done Andrew, i really like that.

As always though....a few questions if i may.

Roughly what size is the unit, and what sort of bearings where they, standard ball, deep groove etc? How have you eliminated endplay?

I have wanted one for a while but they always fetch a fair bit of money. I do however have a small 180v DC motor (when i say small, i mean small package, its 1hp) and all the control gear left from the failed lathe conversion. This with its original multi v belt and pulleys reversed might make the start of a nice little unit. The DC motors are very smooth.....

I'd say it depends on your lathe. If you want it to last forever then maybe not. If its "replaceable" like mine then I wouldnt worry so much.
I've used aluminium foil held in place magnets when turning cast and that seems to work well enough. Careful of how open your spindle bearings are.

Stuart

Thanks Guys.

It sounds like I may be OK as long as I can keep the grit away from the bed and slides.
I'll be stocking up on rags, paper wipes, aluminium foil and maybe set up some sort of telescoping sheet metal bed guard, possibly.
The lead screw has a metal cover so that should help there.

Bob,

in the picture of the test piece, you can see the chattering from an earlier grinding attempt done before the wheel was dressed, and using power feed (spur gears etc.). The dressing removed the vibration and other harmonics, and using manual feed gave the good finish at the end of the test piece.
I don't think these bearings will hold up at 38000RPM for internal grinding...

Rob,

Some good ideas there for thought, to make the TPG more versatile.
I'm not sure if the motor would be powerful enough to use a thin cut-off disk though. Worth a try.

Ueee,

The bearings are just standard groove single metal shield ball bearings from an old electric motor that had very little prior use (shields on the outer ends of the bearings to reduce grit entry). End play in the housing is eliminated using the spring wave washer from the old motor, but internal play in the bearings is not preloaded out so the shaft is not perfectly located axially (if that makes sense).

Base plate is 110mm wide x 170 mm long, spindle housing is 105mm long and 32mm diameter, input shaft 9mm dia and output shaft 12mm dia. Wheel bore ended up at 1/2" doameter so there is a VERY thin tube between the shaft and the wheel bore(That was delicate to machine in aluminium)

These bearings were used as this was more a "proof of concept" than something expected to be used in a big way, but it seems to work better than I expected.

Andrew

Originally Posted by Stustoys

I'd say it depends on your lathe. If you want it to last forever then maybe not. If its "replaceable" like mine then I wouldnt worry so much.
I've used aluminium foil held in place magnets when turning cast and that seems to work well enough. Careful of how open your spindle bearings are.

Stuart

I agree on both counts Stuart.

Regarding the headstock bearings,my Chinese lathe does not have a lip seal to protect the front one, only a basic metal cover.

I had the spindle out last year to grease the bearings and you can see a wear pattern on the first 4 - 5 mm of the tapered bearing cone from (I presume) grinding grit getting in past the cover. So that's an example of what can happen if you don't cover up.

A thin cutting disc (small diameter) won't put any more load on the grinder than a wide stone if fed in correctly.

You really should eliminate TPG end float if you use these (for safety reasons as well as work finish).

Cheers

Rob

Originally Posted by nearnexus

You really should eliminate TPG end float if you use these (for safety reasons as well as work finish).

Rob,

I'm not sure if I explained what I meant very well.

The inner race of the wheel-end bearing is locked on the shaft between the step in the shaft and the inner wheel clamping flange extension, so there is no float there.
The outer race of the wheel-end bearing is located in the housing clamped between the step (face) in the housing and a wave washer compressed by the housing end plate.

The pulley end bearing floats axially within the housing, and resists radial load only.

The only float is within the ball bearing itself (balls to races side tolerances, wear).
I'm not sure how much axial pre-load these standard bearings can take before enough is too much, but I doubt it is very much at all. There is no obvious end play on the shaft, although I haven't checked with a dial indicator.


Andrew.

Originally Posted by mahgnia

I'm not sure how much axial pre-load these standard bearings can take before enough is too much, but I doubt it is very much at all.
Andrew.

I was surprised to find standard sealed ball bearings on the steering stem of some motorbikes - Norton Commando, MZ ETZ250. Both these used a tube between the top and bottom inner races. They weren't necessarily pre-loaded, but had to take road shocks "side on". They were trouble free in this application.

Jordan

Originally Posted by nearnexus

.

Regarding the headstock bearings,my Chinese lathe does not have a lip seal to protect the front one, only a basic metal cover.

I doubt any lathe of any decent design uses lip seals in the spindle... They all use labyrinth seals... lip seals create friction, that create heat which makes the spindle expand... Not what you want to happen...

Originally Posted by mahgnia

Rob,

I'm not sure if I explained what I meant very well.


Andrew.

Hi Andrew,

I totally understood what you meant, I'm just pointing out that any freeplay (eg from wear) is unacceptable. My TPG has caged (magneto) bearings on the quill spindle and adjustable side thrust caps.

As far as making your own TPG goes, some people use a cheap wood router as the drive unit.

Regarding sealed bearing side thrust limits, correct me if I'm wrong, but I think pillar drills only use sealed races in the quill ?

Cheers

Rob