PDA

View Full Version : Center finder - wiggler style



Fasttrack
08-21-2008, 01:13 AM
As I home in on my DTI, I was thinking about other knick knacks I've been meaning to get for awhile now. (I got a bit of a "bonus" from work this summer so its off to Enco! ;) ) I was thinking about getting one of those wigglers that have a 60* point for centering a hole or center punch mark. Its much cheaper than a coax indicator and I don't expect it to be near as accurate. Currently, my method of lining up the spindle involves a transfer punch held in the endmill holder or drill chuck depending upon the application and then lowering the transfer punch to the center mark. I carefully observe the punch and adjust one axis until there is no percievable flex in that direction and lock the axis. Then I proceed to the other axis. Obviously not very precise. I'm just looking for something to speed up the process.

Anyway, my question is: how easy are they to use? It seems like it would be hard to get both axis centered unless it jumped for one axis and then jumped for the other, but I don't see how it could do that so...

Any thoughts are welcome! Maybe I'll just have to save up for a coaxial indicator.

small.planes
08-21-2008, 03:12 AM
have a look here (http://www.homemodelenginemachinist.com/index.php?topic=2656.0) might give you some answers. Ive got the Starrett Wiggler set, which has a ball end, a disk end and a pointy end. dead easy to use and very accurate, One of the parts I make has opposing counterbores for bearings, so you have to machine one side then flip it and machine the other side. as long as Im paying attention the bearing pockets line up spot on for the shaft.

Dave

Peter S
08-21-2008, 07:34 AM
Fast track,
I am not sure what you mean, but the pointed attachment in the multi-part wiggler set is used (by me anyway) to centre the spindle over scribed lines (not centre punched). This is done by first getting the point running true (thumbnail or 6" rule) and using a magnifier if necessary, not by trying to actually run the pointed attachment into a centre punch.

Actually I seldom do this, I always if possible use the ball-ended attachment and locate off the edges of the workpiece, then move in the required amount - more accurate and no scribing required. However, there always are jobs where you don't have datum faces to work from.

I also have one of the other types of edgefinder (the type with the spring inside), one end is pointed, but I doubt it is intended for ever touching the workpiece (I predict a short life). I think the fact that it can "wiggle" is to allow you to get it running exactly true, no matter how bad your chuck is etc.

For centring on existing holes I use a lever type indicator with attachment for holding it in the spindle, this is excellent and accurate and very useful for other jobs as well. I have to admit I haven't used a coaxial indicator, but seem to get by without one quite well! :)

oldtiffie
08-21-2008, 08:37 AM
Peter,
I think that what was intended was to lower the point into the centre-punch (with the spindle stopped), raise then start the spindle and theoretically, the "throw(-off)" will have a radius equal to the misalignment between the "pointer" and the spindle axis. This pretty well relies on the point of the centre-punch being sharper than the pointer and that the hole/line etc. centre-punching is accurate. A "big ask".

I'd agree with you though. Run the spindle at ~800RPM,and centre the pointer/finder by thumb-nail/ruler until about "right" and "eye it in" as the oscillating pointer will make it that much easier.


I also have one of the other types of edge-finder (the type with the spring inside), one end is pointed, but I doubt it is intended for ever touching the workpiece (I predict a short life). I think the fact that it can "wiggle" is to allow you to get it running exactly true, no matter how bad your chuck is etc.

Same here. I get it running true, stop the spindle, lower the spindle (and finder) and centre it in the hole by eye. Its surprising how accurate the eye can be with "boning-in" and centering. 10 thou gap on one side and 20 on the other is immediately obvious. I can with get within "thou's" easily.

Same applies to "splitting and dividing" lines and spaces on a ruler. I prefer a Carpenters metric folding rule.They are very accurate and well marked in black on a white back-ground (the ultimate contrast). I can "split" a mm - by "eye" into as many parts as I like. Beats Engineer's rules every time.

The "Mark 1 Eye-ball" is a truly remarkable instrument.

I too get by very well with a good TDI in the spindle/chuck/collet as well when it comes to centering on holes.

John R
08-21-2008, 09:13 AM
I use mine by lowering the point into the punch mark and then moving both axis untill there is no offset between the main shaft of the tool and the moveable part that is inserted into the punch mark. It is easy to feel the offset with your finger. Just slide your finger up and down across the joint in the tool in both axis.
Good luck
John R

oldtiffie
08-21-2008, 09:32 AM
Thanks John.

I can see that will work.

The main problem is that even if that is 100%, there are doubts about some marking-out if done with a rule instead of a scribing block or equivalent or better in the first place and that the centre punch mark is accurately on the line.

Bill Pace
08-21-2008, 10:17 AM
I use mine as described by John R....

Mind you, this was arrived at by my own thought processes -- being self taught (took me forever to find out that the needle & ball points attachments would "kick" to give the edge!) On the couple units that I have - a Starrett & a Chinese - the 60* point doesnt want to be put in the center by holding with a finger, will drift slightly off very easily, consequently I assumed that method wouldnt work, but by lowering it gently into the hole or dimple and doing as John describes, it will quickly line up.

Would not any thing that had a point on it accomplish what y'all are describing? Isnt the whole purpose of the spring action to allow movement? and give you the ability to move the part under the point till it is true?

Hopefully some more of the real seasoned guys will come in here and offer more input on this --- might learn something;)

JCHannum
08-21-2008, 10:32 AM
The Brit's use a devise called a sticky pin in place of the Starrett 828 type wiggler.

It is basically a gob of something tar like on the end of the end mill. A needle or pointed rod is jammed into that and centered up with the spindle rotating at a low speed. It is then used to locate a center punch mark or scribed center mark.

There is a difference between a wiggler type center finder and an edge finder. Both will serve the same purpose in many cases, but each has it's own advantages and disadvantages. I use the wiggler most for indicating a center spot or scribed line, but do not contact the work with it. The added length of the pointed rod makes seeing the target much easier than the pointed end of the edge finder.

RPM
08-21-2008, 01:17 PM
I use the Starrett pointed wiggler on a daily basis, for accurate lining up of a heavy Delta Rockwell drillpress over an x-y adjustable vise. I run it at my lowest speed, about 400rpm, and lower the tip carefully into a prick-punch centre hole on scribed lines on the workpiece.

Of course, it all depends on the accuracy you need. If I use an optical centre punch, or the prick-punch and a maginfying glass for the layout, and use a magnifier to centre the workpiece, I can get to 1-2 thou accuracy repeatably. But to do this you have to have good close vision, as you need to detect the tiny offset movements of the wiggler as it slides into the centre punch hole.

As usual, with practice it becomes second nature, and it's nice to have holes where I want them. But if you need better accuracy, you'll have to use an edge-finder.
Richard in Los Angeles

lugnut
08-21-2008, 03:16 PM
Little machine shop has this wiggler info

http://www.littlemachineshop.com/Reference/Wiggler.php

Mel

Fasttrack
08-21-2008, 06:51 PM
Hey RPM - thanks for the distinction with prick vs center punch. I got the impression that the "center finder" with a 60* point could be used as you describe, dropping it into the 60* divet made by a properly sharpened prick punch. The center punch is supposed to have a 90* and I usually just hand sharpen those. No telling what the angle is :D

Just lining it up optically is what I do now, basically. I just rely on the accuracy of the point on a transfer punch. I'm assuming that it is concentric and centered to the outside diameter. Again this is for rough work so I think, for the money, I'll buy one. (I'm looking at rebadged ones, like Fowler or even B&S has some pretty cheap ones, as in <10 bucks)

lane
08-21-2008, 10:33 PM
No get a Starrett. are find a Lufkin. You want one that the ball will snap out of .some dont . Some you have to unscrew to change ends.

Peter S
08-22-2008, 07:55 AM
The Brit's use a devise called a sticky pin in place of the Starrett 828 type wiggler.

JC,
Not just Brits. The sticky pin is not necessarily a wiggler replacement, it is an additional tool. The sticky pins main use in my experience is for when you have a milling cutter in your collet, and you want to centre over some lines. It is much quicker than having to fit a wiggler, you simply slap the sticky pin onto the end of your cutter and centre it while running, as you would a wiggler.

Actually, its main use I find is not for centring, but for when you want to move your work piece around on the table and align it with an axis. No attempt is made to centre the pin, it is simply stuck onto your cutter, the spindle left stationary, and it acts merely as an instant sharp point. You run the sticky pin up and down a scribed line or feature and then clamp your job down.

The normal sticky pin around here is a lump of plasticine with a needle or pin embedded, they are usually found permanently stuck on the turret head...

As for you guys who are trying to pick up centre punches with your centre finder....I recommend you simply locate the intersection of your scribed lines, much more accurate than a centre punch.

Swarf&Sparks
08-22-2008, 08:05 AM
FWIW, I'm well pleased with the coax from LMS.
Had it a year or so now. No mill at home yet, but it makes life easier on the 4 jaw setups and the DP.
Also mount it in the lathe tailstock for checking radial and axial run out on bores (as opposed to drill holes) ;)

Peter S
08-22-2008, 04:39 PM
For picking up a centre punched location, you could use a piece of steel rod with a point turned on one end, hold this in the drill chuck. Hold it down into the centre punch and tighten down the work piece. This is not particularly accurate, but has its place. I have silver steel (drill rod) hardened for this type of job.