lathe boreing

[buford2]

lathe boring

Project....4130 cold drawn seamless tubing.
2.718 OD
2.375 ID to finish at 2.396
26" long
Objective... to finish bore ID of tube with little or no chatter. No machining lines that can be felt with finger nail.

Thank you for any help you can give.

 

[JimDawson]

I would ream that one. The other option might be to build a boring bar with the minor diameter on the end as a guide, then offset the bit the proper amount. This would support the bar in the bore. The other option would be to ream then hone.

 

[Wreck™Wreck]

Re: lathe boring

Project....4130 cold drawn seamless tubing.
2.718 OD
2.375 ID to finish at 2.396
26" long
Objective... to finish bore ID of tube with little or no chatter. No machining lines that can be felt with finger nail.

Thank you for any help you can give.

A 26"deep bore? That is nearly 11:1

 

[buford2]

Re: lathe boring

Could you explain 11:1 please.

 

[Wreck™Wreck]

Re: lathe boring

Could you explain 11:1 please.

It is the ratio of bore diameter to bore depth.

A 1" dia. bore 1" deep is 1:1, a 1" dia. bore 2" deep is 2:1 an so on.

 

[NightWing]

Re: lathe boring

How many parts to make? Tolerances? Concentricity? A reamer that size would be very expensive. Sounds like a good "no quote" job.

 

[buford2]

Re: lathe boring

10 pc order. Potential for good volume in 10 to 15 pc orders.

 

[JimDawson]

Re: lathe boring

You might take a look at this http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=951552&PMAKA=334-1120
For low volume this might work, but I would consider getting a carbide tipped shell reamer ground to size.

 

[Round in circles]

Re: lathe boring

26 inches .. " Shot gun barrels ! " .

When shotgun barrels used to be hand made they were eventually cold drawn internally .

They used to be set to the final size by drawing or pushing a series slightly differing diameter / sizes of well lubricated steel ball bearings in a cup on the end of a rigid bar or welded or threaded on to a long threaded rod that was pushed or pulled through the barrels till the required bore size is reached . There are no marks left in the barrel , You needed to make sacrificial end caps to keep the ends of the tubes true .

Could you perhaps turn up or grind up some high quality steel and make " small cones with a tiny curvaceous lip or two at the correct size and do the above to the tubes with them , as you only have a smidgeon of differences in the internal diameters ...so long as changing the external diameter a tad is not a problem ?