Broke the Edge Pro Tram

[Conrad_R_Hoffman]

Well, I just busted the shop's Pro Tram. New indicators aren't too expensive, but I wanted to give a heads up about how easy it is to wreck these. Unlike most dial indicators, these run out of travel before the removable tip hits the barrel. Internally they have an anti-rotation screw that comes off the spindle and runs in a slot. If you push the spindle in too far (I hit it with a drill press table that got away from me) the screw will hit the end of the slot, and break off. It's hard as glass, so you might be able to remove and fix it, or not. It also attaches to the return spring.

An easy mod is to machine a small tube that just fits over the spindle, so the removable tip hits the tube (that hits the barrel) just before the internals get over-stressed. That would make the unit as rugged as one would need.

[spro]

Bad it happened yet good advise to others. You explained it well enough that it could happen in similar situations. Yes, a collar or sleeve to prevent that travel damaging the mechanism.

[earlgo]

Been there, done that. I fixed about 4 DTI's that I over stressed a couple of years ago. It is a relatively simple, but exacting task to open up the case, 'drive' out the broken stub, replace it and reassemble. One has to be certain the shaft has not been bent, but that can be 'adjusted' too. Be careful of the springs as they are fragile.

All of the DTI's were damaged by my cheapo DRO on the mill.


Later, I changed the bracket and made it longer so it hit the stop first. DUH.
Someone else suggested the clever idea of using a magnet for the stop so it would be pushed out of the way.

--earlgo

[pete]

FWIW,
Maybe the camera shows your D,I. aligned worse than it really is Earl. But unless your dial indicator is square to your travel within a few .001 you just won't get a correct and accurate travel measurement. Until I can afford a proper DRO I'm stuck using the same method along with a set of Starrett 1"-12" micrometer setting rods. It works,and it works quite well I think,you do need to be a bit careful. But it's sure a slow way to work. I do have to keep reminding myself that at one time it was about the state of the art method for even jig borers, and there was some unbelievably complex yet super accurate work done in that way. Some of it I very much doubt I could duplicate today even with the very best of DRO's available now. On maybe a Moore jig borer in top condition it could be done, but not a hope on my Bridgeport clone.

Somewhere there's an online website that show's 7 plates that had a set of bolt holes precision bored on 7 different jig borer's done by 7 different operators in 7 different locations.Brown & Sharpe or maybe Pratt & Whitney? jig borer's possibly? A well known machine tool manufacture anyway's. But according to the advertisement only one single plate had a single hole out by a few 10ths that prevented a high precision hardened and ground pin from dropping into every single hole in all 7 plates. That test would be very hard to replicate today unless you specifically targeted very high precision company's and well known highly qualified operators just like they probably did back then. I seem to recall that test was done sometime in the mid 1930's if my memory isn't faulty?

Pete

[earlgo]

Conrad: Sorry to have changed the course of the thread.

Pete:
Here is the revised DTI holder.

It is straighter and easier to adjust. It can be seen that the mounting bracket reaches further than the rod guide on the DTI frame.
I use a 1-2-3 block if longer reaches are required, but your idea of setting rods may be more accurate. (I'm with the school that measures with a micrometer, marks with chalk, and cuts with a felling axe, then curses the bad luck.)

--earlgo

[tornitore45]

No one can beat the way I clobbered one DTI.
I was straightening a rod mounted in the chuck with the DTI in the toolpost pushing away an springing back see if the reading got better.
It occurred to me that is the pushing slipped the DTI would be toasted, the very thought made the pushing slip...you can imagine the result.

It goes to say most of the times we know the set up is an accident waiting to happen.

[pete]

Looks good Earl. And with a pair of 1"2"3" blocks you should be good from zero to 6" Your use of the 123's is a bit more user friendly system than those micrometer setting rods though. They really do need some type U shaped sheet metal holder at each end of the rod so there kept square and aligned with the spindle's C/L on the indicators.

Pete

[Conrad_R_Hoffman]

Got the replacement indicator. They changed the design a bit so a more positive screw stops the spindle, but it's still not as good as letting the tip hit the barrel. They also made the indicator half as sensitive! The original had wide thousandths and half marks, about 6 turns full range. The new one has no half tics and is about 3 turns full range. I suppose for $14.99 I shouldn't complain, but the other guy in the shop took a shot at fixing the old one and got the broken screw stub out, so we'll probably use that one- this time with a protective sleeve!