Thread: How do you centre bar for slotting in the mill (or shaper for that matter)

Hi Michael,

How about a wiggler?
I've not used the ball end horizontally but I'd think it would work, Doesnt solve your backlash problem though. The point works fine in the lathe so you could use that to set up off a scrib line or mill the smallest flat you can and center on that?
Shaper I'll have to give more thought to but you can bet there is a simple way out there.

Stuart

Can't you centre the stock with your pointy thing and ruler, then swap the pointy thing for the slot cutter?

Hi Michael, I have a small horizontal mill and I have used the y jigger that you mentioned, how ever it all depends on how accurate the y Jigger is, and I set it up in the collet ,and get the work centred, remove the y piece and install the cutter without moving the work piece and all should be right, but it would depend how accurate you need to be, all though I made mine I have not had to do such work that it would need to be in the 1/2 thou of centre, but have found it very handy for drilling holes and key ways in models, and the odd jobs ,hope this will help. Eddie

The slotting cutter is a disc type on a horizontal arbor.

Originally Posted by Stustoys

Hi Michael,

How about a wiggler?

Stuart

A wiggler will work on a vertical axis. but I think gravity will have something to say about it working accurately on a horizontal one

Originally Posted by jack620

Can't you centre the stock with your pointy thing and ruler, then swap the pointy thing for the slot cutter?

As above, it is a cutter on a horizontal axis. I could swap the disc for a dummy one with a V edge, but I then have to rely on the central plain of the cutter and the disc being in the same location - No good if my dummy disc is say 3mm and the cutter say 1/4"

Michael

I have not needed to do it accurately yet but I think I would advance (Y-axis) the table/stock towards the lowered saw blade (raised table) and set the gap between flat side of blade and side of round stock with a feeler gauge. The feeler gauge should compensate for the offset teeth if used against the flat side of the blade. Then just the old half the diameter plus the feeler thickness plus half the thickness of the blade flat section trick.

All movement is in one direction so the backlash should not be a problem. If I did the same on my mill of course the blade would be horizontal and the measurement point would be the top of the stock. The same situation, just a different and not so easy viewing angle.

I did drill some 50mm rhs yesterday using this method (sort of) but with a strip of paper instead. It was only for some pivot bushes so did not have to be perfect.


Dean

Sorry Michael,
Missunderstood what you were doing.

Square on the table against the bar, feeler guages to the cutter, repeat on other side. Stuff about as long as you want until you are as close as you want.

Stuart

OK, so it's like a Woodruff cutter? If so, this video might help. He's using a Woodruff cutter in a lathe with a milling attachment. Tune in at 7 minutes to see how he centres the cutter on the round bar.

http://youtu.be/Boov7h6dr20

Apologies if this isn't what you are trying to do.

Chris

Hello Michael (& the others),

The inverted 'Y' seems to be the answer, but if the 'V' isn't perfectly in the centre of the Y-tail, then it will be a problem.

If it isn't perfect, then resting the Y in the chuck/collet, measuring, then rotating the Y 180 deg & re-measure will quickly tell the lateral error - move the slide 1/2 the error.

I'm not sure what level of accuracy that might achieve, but the same check/measure process while machining the V into the 'jigger' should be able to ensure accuracy of the 'jigger'. Any (significant) error after that should only be as a result of inconsistencies within the workpiece/s.

...Now I will have to go make a 'jigger' ...
Daryl

Originally Posted by DarBee

Hello Michael (& the others),

The inverted 'Y' seems to be the answer, but if the 'V' isn't perfectly in the centre of the Y-tail, then it will be a problem.

If it isn't perfect, then resting the Y in the chuck/collet, measuring, then rotating the Y 180 deg & re-measure will quickly tell the lateral error - move the slide 1/2 the error.

I'm not sure what level of accuracy that might achieve, but the same check/measure process while machining the V into the 'jigger' should be able to ensure accuracy of the 'jigger'. Any (significant) error after that should only be as a result of inconsistencies within the workpiece/s.

...Now I will have to go make a 'jigger' ...
Daryl

I don't think it will work. The mill is a horizontal.

Hi, on one of his Youtube videos Keith Fenner was cutting a keyway in a shaft using his K&T 2H horizontal mill, but using a vertical head attachment (I think from memory). This method should work either way, using a vertical head or just using the horizontal arbor with appropriate cutter.
Firstly he clamped the round bar down in a T slot on the bed, so that the bar to be slotted was held parallel to the x axis. He then gradually raised the table toward the cutter, having eyeballed the workpiece being central to the cutter. As he slowly approached the cutter, eventually the cutter kissed the workpiece, and at this point he moved it back and forth in the Y direction, gradually increasing the depth of cut. When he had the machined section on the workpiece as wide as the cutter, he centred it by eye below the cutter, locked the Y axis, and began to cut his keyway. He shows it much better than I can tell it, but it would take me a fair while to find the right video again, otherwise I would post the link. For those unaware of Keith Fenner, he is one of the best and also one of the most prolific machine shop Youtubers out there, and well worth looking at. Be warned though, watching him is very addictive. Here is an example of one of his episodes. Neglect - YouTube. HTH,
Rob.

Is your slotting cutter large enough to reach more than halfway down the side of your stock.If so use a piece of paper,bring the cutter in until it just starts to pull the paper out of your hand,then just keep moving the cutter until its in the centre of your stock,of course you would need to measure your cutter and stock to get centre,if that particular you can measure the paper and allow for that as well.

Do you have a angle plate that is higher than you stock when set up,if so place the angle plate against your stock and use either a set of inside calipers or verniers or telescopic gauges to set your cutter in the centre of your stock,if you don't have the angle plate you could use a heavy parallel or even an engineers square.

For getting close just use a rule in the above example.

For setting centre in the shaper you can use the paper between the side of the tool and the stock.

For some reason I was thinking of a slitting saw. Go with Pipeclay's method then.

Dean

Hi Michael,
I use the paper method but the paper is a cigarette paper. Normally they are about 0.0015" thick so when the cutter grabs the paper you are within that distance from the side of the work.
This method has worked beautifully for a lot of years.
If the work is too large in diameter to get the cutter down the side then I do as Stuart said and use a Square with the paper. You just have to remember to add the thickness of the blade of the square to the distance you move the cutter over (or table under). This way backlash ceases to be a problem because you only travel in the one direction.

Phil

Originally Posted by Steamwhisperer

Hi Michael,
I use the paper method but the paper is a cigarette paper. Normally they are about 0.0015" thick so when the cutter grabs the paper you are within that distance from the side of the work.
This method has worked beautifully for a lot of years.
If the work is too large in diameter to get the cutter down the side then I do as Stuart said and use a Square with the paper. You just have to remember to add the thickness of the blade of the square to the distance you move the cutter over (or table under). This way backlash ceases to be a problem because you only travel in the one direction.

Phil

This is also how I do it for fussy work. The old cigarette paper trick.

For less fussy work I traverse the cutter while running using the Y axis until it just kisses the top of the bar. As soon as you have a flat spot the width of the cutter or *very* slightly larger, stop. You can now centre the cutter very accurately using the Mk 1 eyeball.

This also works for vertical mills centring slot drills etc. It's my standard way to set up for cutting keyways in fact and I've never had a binding problem due to lack of concentricity. Heaps faster than screwing about with an edge finder, swapping tools, traversing half the work diameter plus half the cutter diameter etc.

PDW