F
Fla mac
Guest
I need some help. What will run truer a shaft in bearings or a shaft in bushings (low RPMs)?
john
Mims, Fl
john
Mims, Fl
JerrySharrett
Senile Member
What are you trying to build? What operating speed, etc?
Runout, of a straight shaft would be based on bearing quality or bushing clearance.
Bushing clearance to a clearance of oil film thickness is probably the most rigid but a bushing/shaft fit would not be able to run at as high speed as a percision ball or roller bearing.
Runout, of a straight shaft would be based on bearing quality or bushing clearance.
Bushing clearance to a clearance of oil film thickness is probably the most rigid but a bushing/shaft fit would not be able to run at as high speed as a percision ball or roller bearing.
4
4Mesh
Guest
The truest way is running on dead centers... or in V blocks. Bearings, bushings, etc, all has slop. If you're looking for something to run really true, rough in a lathe and finish in a grinder. Not everybody's got a nice Internal laying around, but counterrotating is the way to go. (I wish ours was cnc).
F
Fla mac
Guest
Jerry,
I would not get it above 100 RPMs. I am playing something to help in neck turning on a lathe. 30BR and 6BR
John
Mims, Fl
I would not get it above 100 RPMs. I am playing something to help in neck turning on a lathe. 30BR and 6BR
John
Mims, Fl
4
4Mesh
Guest
Well, take a look at the turning tool itself (depending on brand). It's a completely locked-up dead center arrangement. And that's why it's accurate. For neck turning, I'd recommend getting away from your lathe and going to a Lee 3 Jaw Chuck and spinner, in a high torque, low rpm drill, such as a Makita 540rpm VS 1/2" drill.
F
Fla mac
Guest
4Mesh,
I got more time than I do money, just playing in the shop.
john
Mims, Fl
I got more time than I do money, just playing in the shop.
john
Mims, Fl
S
squeakie
Guest
without question angular contact ball bearings; assuming your bearing journals run true and are ground. You should be able to get a pair of ABEC 7 bearings to run within .0003. But for no more load than you are proposing, a simple pair of conrad ball bearings will get you well under .0005" TIR
gary
JerrySharrett
Senile Member
John. I don't follow. If you are neck turning on a lathe, the best way IMO, you are stuck with what the lathe was built with. If you are getting chatter you probably need a spindle bearing or bushing adjustment or you have crappy bearings.
F
Fla mac
Guest
Jerry,
The lathe I 'm using is a SB 9, flay belt. I am sure it is not that good, just something I wanted to try. I will start with some 243 brass and see what the necks look like. Like I say I have more time than money. Most people turn the brass at the head stock, but I want to see if I can set it up to turn it at the tail stock and hold the base of the brass at the head stock using a K&M brass holder modified with a pin that goes in the primer pocket.
john
Mims, Fl.
The lathe I 'm using is a SB 9, flay belt. I am sure it is not that good, just something I wanted to try. I will start with some 243 brass and see what the necks look like. Like I say I have more time than money. Most people turn the brass at the head stock, but I want to see if I can set it up to turn it at the tail stock and hold the base of the brass at the head stock using a K&M brass holder modified with a pin that goes in the primer pocket.
john
Mims, Fl.
JerrySharrett
Senile Member
John your SB-9 has sleeve bearings and will turn case necks much better brass than any other method. Each time you turn a batch, make an arbor. On the arbor the smallest diameter. about 3/16" long will be just a few thousands under bullet diameter. Then next diameter moving toward the chuck will be exacty bullet diameter and 1/16" or so longer than the case neck. The next diameter toward the chuck will be about 0.0005" smaller than what you are turning the necks to. The middle diameter in being exactly bullet diameter allows you to turn the neck to exactly what it will when the bullet is seated..
You need to use your K&M to push the cartridges on the arbor and make it into a slide hammer to get them off.
This is an arbor. This one looks kind of rough to start since it is made from an old Class 8 5/16 bolt;
This is a neck being turned; Notice the tool is parked over the third diameter.
This is the K&M made into a slide hammer; Use it and the tailstock to press the case onto the arbor, then use it as a slide hammer to pull the case off.
I rig a 0.0001" dial indicator directly to the tool post to make it simple to set the diameter.
This is not the only method but one of the better ones to turn case necks on a small engine lathe
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F
Fla mac
Guest
Jerry,
Do you use a live center in the primer pocket to hold the base of the case? And do you set your compound tool holder to 28 degs? When I use a K&M turner and a drill the case neck gets hot (or warm) with each case I turn. I lub everything good and run the drill slow. I will post some photos on what I an doing. I do thank you all for the info I have received. I will keep you all informed on how my tool works.
john
Mims, Fl
Do you use a live center in the primer pocket to hold the base of the case? And do you set your compound tool holder to 28 degs? When I use a K&M turner and a drill the case neck gets hot (or warm) with each case I turn. I lub everything good and run the drill slow. I will post some photos on what I an doing. I do thank you all for the info I have received. I will keep you all informed on how my tool works.
john
Mims, Fl
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Boyd Allen
Active member
When turning on the lathe, using the method shown in the previous post, the case turns with the mandrel, so there is no rotating friction between them to cause the heat that you got with your drill press setup. If the case has some wobble at its base, it is of little consequence. It is secure enough for turning because of an interference fit on the turning mandrel in the chuck.
N
NesikaChad
Guest
Here's a thought/idea:
First a little theory (dissertation):
The whole preface around accurate gunmaking (as it pertains to actions/barrels) begins and essentially ends with the bullet's rotational center of the barrel (and the action right?) We want our chambers concentric with the hole already in the pipe and we want it to screw onto the center of the hole that the bolt travels inside of. Assuming the firing pin hole is/was made right we want it in the middle too.
Take one little step back for a moment and look at the big picture. The chamber is cut. With any luck it's in the center or at least dern close to it. What does this mean for the cartridge going into it? It means it's going to register into what is already there. If for instance the chamber was running out by .002" then regardless of how well the brass is prepared it too is going to have this .002" amount of deviation from center.
I say this only to illustrate, it's not meant to suggest neck turning or any other "higher end" brass prep is not needed.
The question my mind leads to with this is:
IF we were to register the rotational center with the bullet then I would jump on the wagon and agree that the mandrel in the neck of the case method for turning brass is viable and the only way to go.
But we can't do that. The bullet is just along for the ride.
The OD of the case is what locates the cartridge in the chamber. The bullet is inside (part of) the cartridge.
So from my little world it stands to reason that captivating the outside of the case in a simulated chamber (meaning a die with the end whacked off to expose the neck area) and then BOTH turning the OD of the neck and single point boring the ID is the only really accurate way of ensuring the bullet is going to run in the theoretical center of the chamber. This is regardless of the clock position.
I qualify this with a gross exaggeration:
Take a neck mandrel and clamp it in a vise. Now grab a virgin piece of brass and insert it onto the mandrel. Now push on the rim of the base to bend the neck into some obscure angle.
Now take that piece of brass and neck turn it with whatever fancy tool your hard earned money bought for you. Now insert a bullet and stick it in your chamber runout gauge. It doesn't take a quantum physicist to see that bullet is now wobbling down the road like a Flintstone's tire.
Now if we took that same brass and single pointed the ID/OD I think we'd have a better potential for that little bullet to center up in the pipe.
Just a thought. Comments welcome.
C
First a little theory (dissertation):
The whole preface around accurate gunmaking (as it pertains to actions/barrels) begins and essentially ends with the bullet's rotational center of the barrel (and the action right?) We want our chambers concentric with the hole already in the pipe and we want it to screw onto the center of the hole that the bolt travels inside of. Assuming the firing pin hole is/was made right we want it in the middle too.
Take one little step back for a moment and look at the big picture. The chamber is cut. With any luck it's in the center or at least dern close to it. What does this mean for the cartridge going into it? It means it's going to register into what is already there. If for instance the chamber was running out by .002" then regardless of how well the brass is prepared it too is going to have this .002" amount of deviation from center.
I say this only to illustrate, it's not meant to suggest neck turning or any other "higher end" brass prep is not needed.
The question my mind leads to with this is:
IF we were to register the rotational center with the bullet then I would jump on the wagon and agree that the mandrel in the neck of the case method for turning brass is viable and the only way to go.
But we can't do that. The bullet is just along for the ride.
The OD of the case is what locates the cartridge in the chamber. The bullet is inside (part of) the cartridge.
So from my little world it stands to reason that captivating the outside of the case in a simulated chamber (meaning a die with the end whacked off to expose the neck area) and then BOTH turning the OD of the neck and single point boring the ID is the only really accurate way of ensuring the bullet is going to run in the theoretical center of the chamber. This is regardless of the clock position.
I qualify this with a gross exaggeration:
Take a neck mandrel and clamp it in a vise. Now grab a virgin piece of brass and insert it onto the mandrel. Now push on the rim of the base to bend the neck into some obscure angle.
Now take that piece of brass and neck turn it with whatever fancy tool your hard earned money bought for you. Now insert a bullet and stick it in your chamber runout gauge. It doesn't take a quantum physicist to see that bullet is now wobbling down the road like a Flintstone's tire.
Now if we took that same brass and single pointed the ID/OD I think we'd have a better potential for that little bullet to center up in the pipe.
Just a thought. Comments welcome.
C
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JerrySharrett
Senile Member
John, the case neck is expanded to where it presses on the mandrel. I use an expander that has been polished down to about 0.242". That is why the K&M/slide hammer is needed to pull the turned case off.
The the threaded rod running out of the K&M (pictured) has a center in it and I use the tailstock with a center (live or dead) to press the case on the mandrel with. When finished I just "hammer" it off.
It makes no difference what degree the compound is set on since I don't feed with it. I turn both 30 degree and 40 degree shoulder cases on this setup but the leading edge of the tool is set accordingly even though I don't actually machine the shoulder with it.