Problem indicating receiver threads

[Gazz]

I am attempting to make a copy of the DeLisle Carbine, a SMLE converted to .45ACP and suppressed. The donor rifle is an Ishapore 7.62 NATO that supposedly had a bad barrel and was difficult to open after shooting. At least that is what I was told by the seller who is a friend and somewhat knowledgeable. In any case, the barrel is off and I made an arbor (.583" d) to mount the receiver in the lathe as part of the receiver needs to be bored out as the .45 barrel is set back into the receiver and the bolt shortened. I will be boring out at least 2" of the receiver (starting after the barrel threads end) and want to support the forward end of the receiver with the center rest. I also want to be sure that the receiver is running true and will adjust the center rest to make that happen. My attempts at using an indicator on the receiver threads is not so good. The ball end on the indicator rides on the crest of the thread then of course drops off into the trough as the receiver turns. The measurement shows only one point when the receiver makes a revolution and comes to the crest of the thread again so it's not telling me what I need to know. Any clever ideas on how I can make this measurement short of turning and threading something to screw into the receiver threads for the barrel?

 

[paracongo308]

Why aren't you working off the centerline of the raceway?

 

[Gazz]

I am such a Duh! I think the indicator tip may be long enough to reach in that far. I'll go check it now.

 

[jonesturf]

Are you saying a steady rest (center rest) will support the front end of the receiver? They're not really adjustable without truing the outside diameter to match the centerline you are after. Or you could make a sleeve to go in the steady and hold the receiver...then it would be adjustable if you added some set screws to align the front end like a 4 jaw. Can you fit the receiver inside your spindle bore?

 

[Spyderedge]

Are you saying a steady rest (center rest) will support the front end of the receiver? They're not really adjustable without truing the outside diameter to match the centerline you are after. Or you could make a sleeve to go in the steady and hold the receiver...then it would be adjustable if you added some set screws to align the front end like a 4 jaw. Can you fit the receiver inside your spindle bore?

You mean like a "cathead"? They're used for holding square, hex, and octagional work in steadies.

 

[Gazz]

Thanks for the suggestions and comments!
The indicator will reach the bolt raceway although it is interrupted by a missing 45 degree or so segment but I think I can get it to run mostly true. I understand that the exterior of the receiver might not be concentric with the bolt raceway or the receiver threads. If I cannot get within a thou or two, I'll dig through my stuff as I may have an adjustable type ring that I can use. I am mostly concerned with the boring that will be an interrupted cut, one from the magazine feed area and the other from the ejection port and that the receiver will want to flex a bit. As I write this, I think that centering the receiver to the barrel threads would be best since when I cut the threads and the "extension" part of the barrel, they will be concentric to each other. I don't know if the bolt raceway and the receiver (barrel) threads are concentric but they may be. I only have a 9" South Bend to work with so no, the receiver will not fit inside the spindle. And if you are familiar with the SMLE receiver, you would realize just how big a spindle it would be to accommodate it. This will not be a bench rest type gun and just a range plinker in any case. If you are not familiar with the DeLisle, check this out;

https://www.google.com/search?espv=...KAhUMWj4KHbOnAMUQ1QIIHA#imgrc=2mmxj8hlGPW6dM:

 

[GGaskill]

I have indicated using the threads by engaging the half nut at the proper thread pitch. That way, the indicator stays in the same relative place on the thread. But you have a limited number of turns you can run before crashing.

 

[tdmidget]

Threaded holes are never a datum. You datums should be the receiver face and chamber c/l. Make a mandrel with the barrel thread, Not tight but not sloppy. Make sure the face which would be the the barrel face is perpendicular to the imaginary barrel c/l. With mandrel in the chuck screw on the receiver and now you can indicate everything relative to the receiver face and centerline.If it is out enough to matter,( we're not talking tenths here), then you must decide what will be the easiest to correct. I doubt it needs any correction if it was good enough for the Tommies.

 

[Gazz]

After all your suggestions and my attempts to get it to turn true, I think I am going to make a threaded ring that I can screw into the receiver that will have an od larger than the receiver so that the rest has a place to work off it. The ring will have a hole large enough for the boring bar to pass through.
Also, I think the Tommies had little to do with this rifle, other than the basic design (which they got from an American) and the machinery that made it. It was made in 1967 in India.