Question on cutting a chamber.

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dave_mustaine

Guest
I'm ready to cut my first chamber ever thru the headstock on my Heavy10 and I have a question. I have the bore dialed in to 0 runout when I turn the spindle by hand. Under power, the needle on the dti moves ever so slightly but is still under .0001", I figured this was just from machine vibration. However, when I put the machine in the back gear, I get about .0002 -.0003 runout. I'm just wondering what might be causing this and if if could cause any problems should I decide to chamber in the back gear? Maybe its just extra vibration from the back gear engagment?

The reason I ask is I haven't decided what rpm I was going to try cut the chamber at. It would either be 277 rpm while running on the cone pulley or at 50 or 80 rpms in the back gears. I will be pushing with a Rock Jag floating holder. I planned to try it at 50/80 rpm in the backgear, but may just run at 277 on the cone pulley if it is going to cause a problem in having .0002-.0003 movement while running in the back gear. Thanks fellas.
 
dave_mustaine said:
I'm ready to cut my first chamber ever thru the headstock on my Heavy10 and I have a question. I have the bore dialed in to 0 runout when I turn the spindle by hand. Under power, the needle on the dti moves ever so slightly but is still under .0001", I figured this was just from machine vibration. However, when I put the machine in the back gear, I get about .0002 -.0003 runout. I'm just wondering what might be causing this and if if could cause any problems should I decide to chamber in the back gear? Maybe its just extra vibration from the back gear engagment?

The reason I ask is I haven't decided what rpm I was going to try cut the chamber at. It would either be 277 rpm while running on the cone pulley or at 50 or 80 rpms in the back gears. I will be pushing with a Rock Jag floating holder. I planned to try it at 50/80 rpm in the backgear, but may just run at 277 on the cone pulley if it is going to cause a problem in having .0002-.0003 movement while running in the back gear. Thanks fellas.
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I have a pair of heavy 10's and what you discribe is the nature of these machines. Cut your chamber in low back gear and you should end up with a very nice chamber. These old machines have bronze bearings with two stacks of shim stock on each bearing. Because they run on an oil film they simply can't be set up as snug as modern angular contact bearings which does not mean that they are not as rigid. In fact in most cases they are more rigid. That was one of their main features. If .0002-.0003 is your concern your time would be better spent worring about something else. There is a process of putting a round bar thru the headstock and exerting X amount of lift on both ends of the headstock using an indicator to determine how much shim to remove. This requires a little experience as you have to leave room for oil. Hope this helps.

Last week I had a wreck on my bicycle and broke my right elbow and banged up my right hip. You would think at 72 I'd know better but like they say "there is no fool like an old fool"! Typeing with my left hand takes a while but it's not like I have something better to do!
 
I've come to the conclusion it is just a bit of deflection from having the back gear engaged. No worries. I have shimmed the front and rear bearings to .001 so I know they are good. Can't really do anything else but dial the bore to 0 while spinning by hand.
 
I have a pair of hefty 10's and what you discribe is the nature of these machines.
 
One more thing you can do and it will eliminate the vibration. Get 1140 3 phase 1HP.motor and a VFD and don't use the back gear and you don't change belts anymore. Get a smaller pulley than the large one on the motor and set the VFD up to over speed the motor to 1725 or more. Your vibration is over changing belts is too……. jim
 
I would recommend using a boring bar to do the initial metal removal. Lots less wear on the reamer.
 
jim1K said:
One more thing you can do and it will eliminate the vibration. Get 1140 3 phase 1HP.motor and a VFD and don't use the back gear and you don't change belts anymore. Get a smaller pulley than the large one on the motor and set the VFD up to over speed the motor to 1725 or more. Your vibration is over changing belts is too……. jim
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Very much agree. The VFD lets the lathe run with an infinite speed control and is easily the best thing I've ever done for my H10 lathe.

You don't say whether you're using a spider to center the barrel at both sides of the headstock. If chambering in the headstock without a way to keep the muzzle end of the barrel true the rotation will likely bring some runout to your chuck/chamber end by loading the head bearings laterally, if for no other reason. Think of the barrel as though it was an axle - held on center at more than one location in order to have it run true.
 
Thanks for all of the tips, and yes I'm using a spider on the muzzle end as well. The VFD sounds nice. I will have to move that to the bottom of the list. I do like the fact that its plug and play on 110v. I'm a shooter first and basically just got the lathe to tinker with my hobby. In fact, I didn't know how to power one up until I got this one home a few months ago. I've done just about everything I can do on to this point except chamber a barrel, so I cut my two match rifles down for a set back. They don't really need it but I thought I would be proactive as this will insure I will be good for all of next season, plus it will give me some chambering experience. I've been surprised at how simple this stuff is to pick up. Can't wait to see the results on the range. What a rewarding experience it will be should eveything go as planned. Can't wait to hear the distant steel ring out as a result of something I built myself.
 
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