The lathe bore diameter is important because depending on what you intend to do with the machine it will allow only up to a certain size part being stuck up inside the bore while you machine on the part sticking out of the bore. For instance if you want to chamber a rifle's barrel the part that you machine on would be outside or partially outside the bore and the rest of the barrel will be inside the bore. If your barrel is a huge diameter heavy bull barrel and you have a mini lathe with a tiny bore you are screwed. If you have desires to build PCP airguns your usual diameter of stock is 1.25" and unless it can fit inside the bore you are forced to turn it using a steady rest towards the end of the lathe bed. If your lathe bed is shortish you may not be able to do that either. SO in short the diameter of the bore is very important based on the lathe's intended use. My Engine lathe has a 1.5" bore and my Hardinge turret lathe has a 5c headstock so it can fit collets that are up to 1.125 I believe inside the bore. The larger the bore the more capable the lathe is for typical work but usually the price of the lathe will go up considerably with bore size as the bearings in the headstock get more expensive as they get larger as does the parts necessary to make the spindle and bore. If you have a nice diameter spindle bore you can also make a spider clamp setup on the tailstock end that uses several screws coming in from around the spindle tube that can be used to center the parts you are machining on the tailstock end while you are machining them on the headstock end which allows you to ensure the part is very concentric with the bore... Does this make sense? Peace
Safe Journey Space Fans, Wherever you are....
This message has been edited by Matospeter on Jul 14, 2012 6:53 PM
Perhaps this video will help... In this video he is using a similar lathe to mine and the barrel is inside the meat of the headstock and the chamber area is just outside of his custom built star clamping mechanism which is in place of the typical three or four jaw chuck. It is able to do this because the spindle bore is large enough to swallow the diameter of the barrel. This can also be done(and perhaps more accurately) with the steady rest at the opposite end of the lathe's bed. When I machine my resorvoir tubes I use the same setup as this video only I usually use my four jaw and try to get the tube turning perfectly concentric using the same four screw clamping setup as shown in this video at the opposite end of the tailstock to ensure the entire length of the tube is concentric with the bore of the lathe. Peace
Rob, You Should read the PDF's sent to your e-mail address
July 15 2012, 12:20 AM
about engine lathes and common methods/setups used to operate them to familiarize yourself with the common terms used to describe a lathes parts and features so we can speak and understand the same "language."
I also recommend you use several of the links on the links page to see what kind of tooling is available for your machine to overcome some of your machines limitations as shipped from the manufacturer such as a 1/2" or 5/8" drill chuck with a #2 Morse taper shank for the tailstock to accept bits up to at least 1/2". Some of the smaller machines will have a hard time drilling with a 1/2" or even a 7/16" drill in steel with a small horsepower motor.
There are also many websites that have hundreds of tips on using The Mini Lathe and Mill.
Yes, the hole thru the headstock is a kinda big deal. Right now I have an old Logan 9" with a 25/32" hole thru the spindle. And am looking constantly for something with larger capacity to allow me to not use the steady rest set up.