Rods For Finding Tir?

[great white]

Newb question: I see guys using what looks like round stock to find run out on everything from 3 jaw chucks to collets. This can't just be round bar stock can it?

Are these purchased tools, or at they made?

If they are made, how do you make them without making the rod with the error inherent to the lathe itself?

I've also seen guys make reference to using hydraulic ram rods as the indicator.

Can someone shed some light on the topic for me?

I'm familiar with dial indicators, micrometers and veniers from work (I rebuild turbine aircraft engines) but lathe work is relatively new to me.

 

[janvanruth]

essentialy they are just round bars
round and straight
so its easy to make your own
just turn a bar to a constant diameter and you're done

the error in your lathe while turning the bar will not effect the bar you are making
just turn a bar round and cut it off on the lathe
a round bar turned on the lathe will always be straight no matter how much runout the lathe has

 

[Billh50]

another thing is to pickup a drill blank and use that. They are straight and ground.

 

[JimDawson]

I just kind of use whatever is handy, end mill shank, dowel pin, TG&P shafting. As long as it's round and straight.

 

[EmilioG]

A good gage pin should work also, or the end of a quality drill bit like a Guhring.

 

[jim18655]

Guide rod from computer scanner.

 

[RJSakowski]

I have used wrist pins for this purpose. I have some 1/2", 9/16" and 3/4" pins. Check them for wear. You should see a slightly smaller diameter where the bearing journals ran. Check for roundness as well because some will wear slightly egg shaped. Check them for runout. by mounting in a chuck or collet and measuring. Mark both the collet/chuck and the pin and rotate 180 degrees. If your runout stays in the same orientation, the runout is in your collet/chuck. If it changes 180 degrees, it is in the pin. If it goes somewhere in between, you have runout in both. It is possible to quantify both with careful measurements even though they both have runout. For wrist pins without wear, I have not found any runout measuring to .0001"
For a quick pin, I have found edge finder shanks to run true. For longer pins, I have a 5/8" shaft and a 3/4" shaft salvaged from an old printer and copier. For any of these options, be sure to qualify them as outlined above.

 

[great white]

Guide rod from computer scanner.

Now there's an idea.

I have one I'm scrapping now anyways. It has essentially no run time on the scanner portion, the printer portion went bottoms up. I was going to pull the servos out and dump the rest. I'll have to be sure to pull the rods out too.