Centre finder

Hi

Can anyone recommend a good centre finder for round bar in my mill

Thanks

Dougie

You could make one of these as discussed by Joe Pie Mill indicator holder Stephan Gotteswinter also shows how to use one here Edge finding techniques and he has also done a few videos on making one.

Martin C

I tend to just use an edge finder touching two sides if the bar is horizontal and 4 points if vertical combined with the 1/2 function on the DRO.

Also use one of these on the CNC with a dti

If you fancy a DIY project, I've always liked Dan Gelbart's idea, but not got around to making it yet, though I do have the ingredents.

Bill

The simplest way is just to put a suitable angle-plate or block against the bar and work from that.

For a vertical cylinder I use two angles set at right angles to each other and to the table. Or a Vee-block again set so the Vee- faces are at right-angles to the table.

My favoured method for working back from a datum face is to temporarily clamp a small parallel, even an HSS lathe tool, to the datum but projecting above it, to give a reversed face hence moving the table in a single direction. I repeat once or twice to ensure the same 0 point.

This whether using the DRO or the hand-wheel dials. I choose according to what I think the simpler and more efficient tor the particular task, but also so I don't lose my touch with using the dials.

Stick a fag paper on to the round bar with a bit of spit then run the spinning cutter up to it until the fag paper shifts.

Then add half the diameter of the bar etc etc. Add half a thou for the thickness of the fag paper if critical.

This is my center finder for round items in the mill. Made when an apprentice.

David

You should have had that in for the Stevenson trophy. Not too late for a MEW article.

If you have a DRO then use an edge finder otherwise any of the suggestions. If you want to splash out then a Coaxial Centring Indicator if you have reasonable travel on the Z axis.

Depends on the accuracy needed. I use anything from a ruler, to the 1/2 function, to a co-axial indicator. For accurate work I use a Haimer Centro, works on spigots and holes:

Andrew

David,

I like your centre finder, I never got to make as anything as useful as that during my first year apprenticeship ....last century !!!!

I would like to make one of those...

That device is exactly the sort of project, in my view, that newcomers to our "hobby" could make as it would be useful, quick to make, very cheap to build and a good introduction to metal bashing.

Regards to all

Derek

https://www.homemadetools.net/forum/osborne-maneuver-27357

**LINK**

Further to the link from John Haine about Osbornes Maneuver Marv Klotz has a useful comment for those folk using a single dial gauge / indicator on an offset arm. The disadvantage of this method has always been the difficulty of seeing whats going on round the back.

But Marv says :-

"An added mathematical insight...

If you're centering conventionally, i.e. by rotating a DTI around the stock until you get the same reading at +/- X, +/-Y there's no reason to check -Y which may have the DTI dial facing away from you.

Given cylindrical stock, there's no way you can have the same reading at +/-X and +Y and not have the same reading at -Y."

Dead right and totally obvious but something neither I, or any one I'd met, had managed to think of in over 40 years. You'd have thought it would have made it into a textbook but the ones I've seen suggest mirrors to see behind. Which drove me nuts in nothing flat so I splurged £50 pretty much immediatley the import co-axial meters came on the scne and have never looked back.

Worth noting that with DRO boxes its easy to use the X feed to butt up against a stiff rod in the chuck on both sides at some random Y axis position close to, but behind the centre line, so the DRO 1/2 function gives the X centre line. Knowing the X centre a similar butting up move on the front lets you derive the Y centre line from the measured diameter of the work and the butting up rod.

When using these butting up techniques trapping a 1 thou feeler or piece of dry cigarette paper between rod and stock so its just stiff to pull out is a very sensitive technique for judging position. Probably tenths thou single sided errors and far less double sided becuase the errors subtract.

Clive

I just use one of the centre finders available from suppliers.

All that they consist of is two legs, at 90 dgrees, pivoting on a small arbor held in a drill or collet chuck min the mill.

You ,merely align a mark bisecting the 90 degree legs with a mark on the centre line of the arbor.

If you Google "Chronos, centre finder" you will see pictures of different ones, and then there is the Chronos website, and others. Prices vary from under a tenner to £62 for a Starrett.

Take your choice

Howard.

As will be obvious from this thread there are plenty of devices and methods around. I've got, or have used pretty much all of them except Howards pivoting V at one time or another. Dunno how that one slipped the net!

Basically perm the most appropriate selection from accuracy, ease of use and price depending on what you do, how much time you have to spare, cheaper solutions tend to be slower to use, and how deep your pockets are.

However if I were starting over with the usual neophyte budgetary constraints I'd settle for the "bump and pull a ciggi paper" method whilst putting my "purchase a device pot of money" towards getting a proper DRO scales and console set as soon as possible. A good DRO is win-win pretty much everywhere on a milling machine so a far better bang for buck overall.

I really like my import co-ax indicator but the £60 or so should come after the DRO has been gotten. I could seriously argue that a decent Huffam wiggler should come before the co-axial indicator. Regrettably the less costly wiggler sets tend to be inconsistent in operation and of variable quality.

All of which assumes you already have a lever indicator as shown by David George. Which really has to come first. Davids carrier bar is a nice easy project and very useful once done. Verdict listed a similar, albeit shorter, device but the price wasn't friendly. Mine was used E-Bay inexpensive but I didn't realise how inexpensive until I saw the catalogue price!

Clive

Edited By Clive Foster on 24/11/2022 20:51:00

The pivoting Nee devices rely on the fact that when a round bar is pressed into a 90 degree corner, the corner will lie of the centreline of the bar.

If you want the mathematical justification, in geometry classes we were taught that bisecting the 90 degree angle between two tangents will provide a line on the centre of the circle.

Howard