Thread: Tool Post Grinders - Can A good one be made?

Just to add to Ewan's comments Simon, when I worked out the necessary crowning for the pulleys I made, (because I was not sure that I would fit the large one on the lathe), I worked out what the tangent angle would be if I wanted to do some trick stuff on the mill. Turned out the tangent angle was around 1 degree. If I'd crowned the pulley on the mill it would have been very similar too - the cutter would have removed around a third of the face and then I would have had to blend it.
The edges on my pulleys are only there to prevent the belt flipping off when things are not rotating - other than that I expect the belt will ride on the top of the crown, even if it is only a fraction of a mm.

Michael

Thank you gentlemen, I'd wondered for awhile why some pulleys have both flanges and crown.

Stuart

Originally Posted by Stustoys

Thank you gentlemen, I'd wondered for awhile why some pulleys have both flanges and crown.

Stuart

On my C0 Waldown, only the motor pulleys are crowned. It is a two diameter stepped pulley.

The spindle pulleys are flat and have a flange each side.

Works well. The crowned motor pulley basically sets the belt position.

Rob

Ueee, Michael & Rob, Thanks for the info. So a mathematical approximation to a crown will satisfy the belt then. 1 deg sloped either side from the middle and then nick the top off to produce a symmetrical trapezoid? Simon

Rounded - a corner may cut the belt.

Michael

Yeah round it over the best you can. I have been making rubber wheels so it is pretty easy to do, in ally it may take a bit more time.

Originally Posted by simonl

Ueee, So a mathematical approximation to a crown will satisfy the belt then. 1 deg sloped either side from the middle and then nick the top off to produce a symmetrical trapezoid? Simon

I had to sleeve and crown the largest pulley on the intermediate shaft for my old Schaublin 102.

It was in steel, and I did it by eye, free hand.

I just crowned it until it looked right (same as the rest), but you certainly don't need much to centre a belt.

I did it in small steps starting from each side (did both sides then moved up), worked towards centre (same principle as making a cone), then smoothed out the ridges in one freehand pass with a finishing cutter, and used a fine file and old belt sanding strips to finish it off.

I think I used a 35 degree profiling cutter, same as for making "V" pulleys.

Pretty easy job - came up great.

I practiced on a bit of scrap first, so maybe do that to get the depth/process right.

The pulley surface should be rounded, so I don't like your nip off the top idea,

Rob

Thanks Rob,

I see what you mean, I have been thinking a bit about it this morning. I have been trying to approach this from a mathematical POV. A height difference of 1/8" per foot equates to a segment of a circle with a radius of approx. 3750mm. Not sure how that helps me but it's a start. I'm trying to work out the DOC and angles required to approximate a circle of radius 3750 with 5 flat edges to approximate the crest. Then smooth out with emery.

I have just worked out the angle of the tangent from the edge of each side to be 2.67 deg. That's a fair bit off the 1 deg that you guys estimated. I'll have another look…...

Simon

Originally Posted by simonl

Thanks Rob,

I have just worked out the angle of the tangent from the edge of each side to be 2.67 deg. That's a fair bit off the 1 deg that you guys estimated. I'll have another look…...

Simon

Hi Simon.

I never subscribed to the one degree theory. I don't know where that came from.

Certainly the curvature on my C0 Waldown is greater per width, than my old Schaublin.

Modern thin section drive belts can wrap around any sized curvature really.

They are not like the old leather and stiff belts which will ride up on the crown.

The belts on my C0 are actually made of a type of woven fabric (original) and as flexible as a sock .

So I wouldn't get too hung up on the degree of curvature being x or y if you use a modern polyester or specialised belt (within sensible limitations).

Rob

Originally Posted by nearnexus

Hi Simon.

I never subscribed to the one degree theory. I don't know where that came from.

Certainly the curvature on my C0 Waldown is greater per width, than my old Schaublin.

Modern thin section drive belts can wrap around any sized curvature really.

They are not like the old leather and stiff belts which will ride up on the crown.

The belts on my C0 are actually made of a type of woven fabric (original) and as flexible as a sock .

So I wouldn't get too hung up on the degree of curvature being x or y if you use a modern polyester or specialised belt (within sensible limitations).

Rob

Thanks Rob. I do think things a bit too much sometimes but one of the parts I like about this hobby is the mathematics which I enjoy playing with.

Cheers,

Simon

I just took the time to have a good look at the flat belt pulleys on my T&C grinder. Looks like im over complicating the whole thing! These pulleys only have two surfaces, ramped up to the centre and then down. The high spot in the middled is rounded but they are essentially flat with the high spot being about 1.5mm higher tgan the sides. These pulleys are about 1" wide. I measured the angle at roughly 3.5 deg. Think ill just copy these.

Edit: Was having trouble attaching pics from my mobile. Here are the pulleys on the t&c grinder:

20150621_162845.jpg20150621_162658.jpg

Originally Posted by simonl

.......There is also some string attached to the felt wick, does this tuck under the felt tube (top of the casting) and act as the wicking for the lubricant from the felt tube to the spindle?

Simon

Yes.

Originally Posted by simonl

I just took the time to have a good look at the flat belt pulleys on my T&C grinder. Looks like im over complicating the whole thing! These pulleys only have two surfaces, ramped up to the centre and then down. The high spot in the middled is rounded but they are essentially flat with the high spot being about 1.5mm higher tgan the sides. These pulleys are about 1" wide. I measured the angle at roughly 3.5 deg. Think ill just copy these.

Edit: Was having trouble attaching pics from my mobile. Here are the pulleys on the t&c grinder:

20150621_162845.jpg20150621_162658.jpg

Nice little tool in the first photo, you've got there Simon. What brand is it, and where did you acquire it from, please?
Kryn

Thanks Bob.

Hi Kryn. Its a starrett bevel gauge. I inherited it from my Dad. Do not when or where he got it. It has a name on it A. G. Flood but thats not my dad.