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Dee
04-13-2006, 11:58 PM
I am a relative newcomer to milling and I am having a problem with center finding with my Co ax indicator. I probably am doing something wrong?
I put the Indicator in a collet, the part that needs the center located in the vice, the diameter of the hole is about 1/2" by cranking both axis back and forth I can get the needle to less than a 001 movement. So I lock down all the gibs drop the indicator out of the collet, insert my boring head to open the hole out and it is off center by about 10 to 20 thousands.
Can any of you folks tell me what I am doing wrong?
Thanks for any thoughts or advice.
Dee

Gary Helmick
04-14-2006, 12:03 AM
Reindicate after you lock the gibs down. I think you will see that it has moved.
Gary Helmick

Gary Helmick
04-14-2006, 12:18 AM
I guess that was a dumb reply. I should have gone on and said that after you lock down the gibs reindicate and then loosen the gibs a little (not all the way) and do it again and again until you get it where you want.
It is a trial and error exercise.
Gary Helmick

Mark Hockett
04-14-2006, 03:02 AM
Dee,
What kind of machine are you using? If it is a Bridgeport type mill check the head tram.
Mark Hockett

John Stevenson
04-14-2006, 06:46 AM
One problem with these things is that they are so bloody long.
You wind the bed down, fit the indicator, true up, remove indicator then raise the bed to do the cutting but how do you know you are in the same plane as when you indicated.
Mark has a valid point in that if the head is slightly out then any centring is only accurate for that position. Raise or lower the quill or table and the bets are off.

I made one a while ago from a post by Jim Hannum I think it was and to be honest I found it so horrible to use it's thrown on top of one of the lathes somewhere.
No problems with Jim's design it's just that I find it hard to work given the length of the thing.

.

Dee
04-14-2006, 11:13 AM
Thank you guys for the responses, truly a great resourse for a duffer like me!
The Machine is a Bridgeport, I was concerned with movement when snugging down the gibbs so I turned on the DRO and the problem is not there ?
Now I will double check the head tram thanks to Mark & John's reply's
Thanks guys
And yes when it is all together it is pretty long.
Dee

JCHannum
04-14-2006, 11:15 AM
Unfortunately, the import coax indicators usually do not get very good reviews for accuracy or longevity. They just do not seem to be the same quality as the Blake.

Tramming the mill, and rechecking after locking the X&Y axis may help, but the problem may be with the indicator. If possible, recheck the setup with a normal indicator after using the coax without moving anything, just to verify if it is the setup or the indicator.

Yes, John, that was me. The design was not original to me, but from one of the Lautard books, which was from an HSM or Projects in Metal article. They are relatively simple to make, but do have their limitations.

I picked up this one last week, it is made by Precision Gage & Tool Co. It is older, maybe a Blake predecessor?
http://members.aol.com/jchannum/coax

Rustybolt
04-14-2006, 12:00 PM
If this is too obvious I appologize in advance.

Are you rotating the spindle while holding the indicator steady?

Scishopguy
04-14-2006, 02:07 PM
The shop I worked in before my retirement had a Blake Co Ax indicator. It was a neat idea but in practice left a lot to be desired. My biggest problem was that the tips that came with it didn't cover all the ranges of holes I had to deal with. Sometimes the small tip was too small and the large tip was too large and it was quicker to get out the Starrett universal set. Like Sir John said, it ended up somewhere else in the shop not being used.

Jim (KB4IVH)

George Seal
04-14-2006, 02:46 PM
A MichinestMate and DRO works wonders for me.
I get .0005 whice is close enough for the girls I go with.

banjoallen
04-14-2006, 08:02 PM
I had a bad experiance with a Phase 2 co-ax indicator.Had to do with a fan hub. Not fun. It was the indicator. Basically it was junk.We never did figure out how many "bad" jobs went out the door because of it. And it was about the same 10-20 thou. that you see.

Allen