Setting up a toolpost grinder

[badabec]

Hello, years ago I bought a toolpost grinder, it has been at the back of the cabinet ever since.
I have now found a use for it.
Do I set it up with the centre of the grinding wheel at centre height?
Assuming I do, I'll have to make an adaptor to lower the spindle height by about 20mm.

Where is the best place to buy grinding wheels? About 40mm in diameter.

 

[Agroshield]

Here is an observation to ponder.

Let us assume you are external grinding. If the centre of the wheel is at 9 o'clock relative to the stock, looking from the tailstock, every 1 thou you move the cross-slide will take 2 thou off the diameter. If the centre of the wheel is at 6 o'clock or 12 o'clock, you can move the cross-slide an inch and the stock will be reduced by exactly zero.

Do some maths and see what sort of control you need for controlling the cut* and choose a height based on that.

It would be wise to download the Norton Toolroom grinding handbook and it will tell you what all the letters and digits mean in a grinding wheel code. Midland Abrasives have a good selection and will modify stock wheels if required. Dress the wheel frequently, use vacuum extraction and cover everything within a 2km radius.

* if your cross slide dial is 6" diameter, you will be able to resolve 1/4 thou' on it. If it is tiny, you might resolve only 1 thou'. You can angle the compound slide such that 1 thou' increment on that puts on a cut of 1/10 thou' but doing that makes accurate length control a bit tricky.

 

[Seadog]

You can angle the compound slide such that 1 thou' increment on that puts on a cut of 1/10 thou' but doing that makes accurate length control a bit tricky.

I'd have thought quite the opposite. It allows you a lot more movement on the handle for a smaller movement of the head, thus more feel.

Edit: For example, if you set the compound to 60° (from perpendicular, i.e. 30° from the axis of the spindle), you then advance the compound 0.5 units along the X axis which removed 1 unit from the diameter. If you can accurately set the compound to 84.27° you will removed 0.1 per division of the compound which is 0.2 from the diameter.

 

[8ob]

My toolpost grinder is a bit of a clunky old thing and there doesnt seem to be an easy way to mount the thing at the right height, I was wondering if it would stay put if I bolted a tang on the side so it would fit in the toolpost holder, sort of treat it as a lathe tool. Not sure whether it would stay still but it would have adjustable height

Bob

 

[Seadog]

I don't see why not, provided your toolpost and the tang are chunky enough to maintain rigidity and prevent vibration. There are no huge forces acting on it, unless you accidentally plunge the wheel hard into the workpiece.

 

[minimutly]

Whatever, it needs to be below or at least not above centre height to counter any tendancy to self feet - exploding wheels territory.

 

[My Old Landy]

I bought my wheels from these people.
Not cheap but good service and a wide range of sizes.

Products - Grinding Wheels - Select by Size in mm - Midland Abrasives

Grinding Wheels

www.midlandabrasives.com

 

[Agroshield]

I'd have thought quite the opposite. It allows you a lot more movement on the handle for a smaller movement of the head, thus more feel.

Sorry. I did not write clearly. I had it in my head that you might need to grind, say exactly 1" long to a certain diameter (or maybe grind up to a shoulder). If the method you use to put on the feed in one axis (changing the diameter) also alters the tool position in another axis (pushes it further into the shoulder), difficulties arise. I think I should have said that angling the slide is useful for fine control of diameter or length but not both simultaneously.

 

[Seadog]

Yes, you'd need to be aware of constraints on the Z axis as you adjust the feed.

 

[DAPPH]

How do you adjust for wear on the grinding stone as you traverse what you are grinding ?
Is it a case of lots of measurements every few mm of traverse ?

 

[badabec]

I bought my wheels from these people.
Not cheap but good service and a wide range of sizes.

Products - Grinding Wheels - Select by Size in mm - Midland Abrasives

Grinding Wheels

www.midlandabrasives.com

Hello, thanks for the link. I couldn't find a 50mm x 10mm (thick) x 20mm (bore) grinding wheel, so have emailed them.

No name on the machine, it appears to be an Atlas Craftsman toolpost grinder. No idea if they are any good. I paid £120 for it about 10 years ago. Now I just need a smaller, 50mm, grinding wheel.

 

[Agroshield]

How do you adjust for wear on the grinding stone as you traverse what you are grinding?

Precision grinding is not like horsing into a rusty piece of steel with a 9" Makita. Roughing passes first, then light finishing cuts.

The easiest one to discuss is a surface grinder. The wheel is a certain width. When making a pass, you step over maybe 1/4 to 1/2 the width of the wheel. So the leading edge of the wheel removes the most material and wears more than the trailing edge. With a light finishing cut, you will have dressed the wheel beforehand and you work on the basis that wear to the trailing edge is insignificant.

A very good book covering all aspects of grinding is 'The grinding of steel' by Eric N Simons.

 

[Pete.]

How do you adjust for wear on the grinding stone as you traverse what you are grinding ?
Is it a case of lots of measurements every few mm of traverse ?

Grinding wheels wear (or at least should if you use the correct grade) from the leading edge backwards. all you have to do is make sure the wheel is wide enough so you get to the end of your grinding before the wheel has worn the whole width. Choose too soft or friable a wheel and it'll wear out before you finish. Choose too hard a wheel and it'll blunt or load up before you've finished. Get it right and you finish the job with some of the dressed face left.

 

[Agroshield]

Choose too soft or friable a wheel and it'll wear out before you finish. Choose too hard a wheel and it'll blunt or load up before you've finished.

And it is a little counter-intuitive concerning wheel selection: for a hard(ened) material you generally need a soft wheel and for a soft material you need a hard wheel.

Same with diamond disks for a grinder - the best one for granite kerbs will not work well on asphalt.