This isn't a new topic - I had mentioned this a week ago, but it looks as if the original post I posted in was deleted and POOF its gone. Someone asked me about it and I couldn’t find it, so this is mostly a repeat.
I picked up some Thomson 60 linear race rods for a different project and assumed they aren’t that straight, but once measured to see if they might work for an alignment rod for action truing there were a few good surprises.
I have five 1/2”x20“ rods, a 5/8”, and just picked up a 3/4”. There was a Chinese rod, but it’s such bad quality I don’t even want to mention it.
The v blocks to measure runout are 12” apart and shimmed up slightly on the outside edges so there’s two small contact points on each end. I realize interpolating between the .0001” marks on the small Federal indicator is not super accurate, but all the measurements were repeatable with two different test indicators and I’d be surprised if a more accurate setup would make much of a difference.
runout at mid span:
1/2”
rod 1: .00005”
rod 2: .00004”
rod 3: .00005”
rod 4: .00002” (!) (Will be used for alignment rod)
rod 5: .00002” (!) (Will be used for alignment rod)
5/8”
.00005”
3/4” (Will be turned down and used for alignment rod bushings)
.00005”
Originally I misspoke and said the 5/8” was the same runout as the Chinese rod, and the 3/4” is a new rod not in the original post.
For anyone not familiar with Thomson rods, they are linear bearing rods, 1566 steel, but widely used as a general purpose industrial shaft with decent strength because of the carbon content and come in different grades, although these case 60 rods have a thick case hardened skin (.040” min), and the spec runout is listed as not more than .001”/12”. Even new prices aren’t bad, but these were all sold as used on eBay, but were not installed.
The 1/2” rods mic’ed dead nuts .5003” from end to end - these may have been a special order since spec diameter range is slightly less than .5”.
The 5/8” was also larger than spec at .6254”, and had the Thomson trademark
The 3/4” was a normal rod and measured .7494”, and had the Thomson trademark
Making bushings is a challenge. Hard turning the case hard exterior slightly oversize and abrasive lapping to size isn’t bad. However drilling the bore, singlepoint boring, then reaming to a slip fit is a chore to get the bore concentric with the exterior diameter. I need the practice, and probably a different reamer.
Anyway, thought someone looking to put together an action alignment setup might find this interesting.
I picked up some Thomson 60 linear race rods for a different project and assumed they aren’t that straight, but once measured to see if they might work for an alignment rod for action truing there were a few good surprises.
I have five 1/2”x20“ rods, a 5/8”, and just picked up a 3/4”. There was a Chinese rod, but it’s such bad quality I don’t even want to mention it.
The v blocks to measure runout are 12” apart and shimmed up slightly on the outside edges so there’s two small contact points on each end. I realize interpolating between the .0001” marks on the small Federal indicator is not super accurate, but all the measurements were repeatable with two different test indicators and I’d be surprised if a more accurate setup would make much of a difference.
runout at mid span:
1/2”
rod 1: .00005”
rod 2: .00004”
rod 3: .00005”
rod 4: .00002” (!) (Will be used for alignment rod)
rod 5: .00002” (!) (Will be used for alignment rod)
5/8”
.00005”
3/4” (Will be turned down and used for alignment rod bushings)
.00005”
Originally I misspoke and said the 5/8” was the same runout as the Chinese rod, and the 3/4” is a new rod not in the original post.
For anyone not familiar with Thomson rods, they are linear bearing rods, 1566 steel, but widely used as a general purpose industrial shaft with decent strength because of the carbon content and come in different grades, although these case 60 rods have a thick case hardened skin (.040” min), and the spec runout is listed as not more than .001”/12”. Even new prices aren’t bad, but these were all sold as used on eBay, but were not installed.
The 1/2” rods mic’ed dead nuts .5003” from end to end - these may have been a special order since spec diameter range is slightly less than .5”.
The 5/8” was also larger than spec at .6254”, and had the Thomson trademark
The 3/4” was a normal rod and measured .7494”, and had the Thomson trademark
Making bushings is a challenge. Hard turning the case hard exterior slightly oversize and abrasive lapping to size isn’t bad. However drilling the bore, singlepoint boring, then reaming to a slip fit is a chore to get the bore concentric with the exterior diameter. I need the practice, and probably a different reamer.
Anyway, thought someone looking to put together an action alignment setup might find this interesting.
