Home lathe precision question

So, what kind of precision can it do? Can it do piston pin level fitting? I don't know what the gap is actually. But things like that, or injector plunger. All very smooth and tight fitting, would a decent home machinist lathe with a person who has good skill, but not god like-can do anything type, be able to do it?

Click to expand...

Short answer, no.
But yes, a talented, experienced machinist can make parts to tolerance on machines not ideally suited for the task, but he'll wish he'd paid the relatively modest cost to have it done correctly.

To do many parts often, automotive machine work on any scale requires specialized machines designed for the task. Everyday production work routinely holds tolerances to .0005" over a set of eight rod bores, pin bores, cylinder bores, block decks, valve guides and if the customer wants to pay a bit extra for it, .0001" can be had. But as mentioned, it's done with hones and surfacers, not home shop lathes and mills.

Random stories:

Before we got a Tobin-Arp rod boring machine, we spent hours making a jig to hold connecting rods on a mill table to bore the small end oversize. Even with all the setup, the results were sloppy compared to what the machine designed for the task can accomplish in a fraction of the time.

With sufficient setup and a large flycutter, it's possible to surface a cylinder head on a vertical mill. On a dedicated surfacer, the head will be on, off and out the door before the guy with the mill can even jig it up enough to begin leveling. The finish will also be correct for the material and the head gasket being used.

Same with cylinder heads with two different valve angles. A head shop will have the seats and guides cut before the guy with the mill can even find the fixtures and clamps to try to get one angle correct.

Don't even think about working with piston pins on a lathe. They're centerless ground and harder than the hubs of hell. It takes carbide tooling and a rigid lathe toolpost to even scratch them.

We work on obsolete Studebaker and Packard engines for which parts are not always available. Another enthusiast designed an adapter to enable an Oldmobile V8 oil pump to be used on the Packard V8. However, he couldn't find anyone to do the manual machining consistently at an affordable cost. The tolerances were just too difficult to hold doing each setup by hand. He asked me to take over the project and I happened to know a talented CNC guy who had a one-man shop. Once this guy did the program, he can run off this complicated part at an affordable price and each piece is dead nuts, when the manual machinist just couldn't do it.

jack vines

Short answer, no.But yes, a talented, experienced machinist can make parts to tolerance on machines not ideally suited for the task, but he'll wish he'd paid the relatively modest cost to have it done correctly.To do many parts often, automotive machine work on any scale requires specialized machines designed for the task. Everyday production work routinely holds tolerances to .0005" over a set of eight rod bores, pin bores, cylinder bores, block decks, valve guides and if the customer wants to pay a bit extra for it, .0001" can be had. But as mentioned, it's done with hones and surfacers, not home shop lathes and mills.Random stories:Before we got a Tobin-Arp rod boring machine, we spent hours making a jig to hold connecting rods on a mill table to bore the small end oversize. Even with all the setup, the results were sloppy compared to what the machine designed for the task can accomplish in a fraction of the time.With sufficient setup and a large flycutter, it's possible to surface a cylinder head on a vertical mill. On a dedicated surfacer, the head will be on, off and out the door before the guy with the mill can even jig it up enough to begin leveling. The finish will also be correct for the material and the head gasket being used.Same with cylinder heads with two different valve angles. A head shop will have the seats and guides cut before the guy with the mill can even find the fixtures and clamps to try to get one angle correct.Don't even think about working with piston pins on a lathe. They're centerless ground and harder than the hubs of hell. It takes carbide tooling and a rigid lathe toolpost to even scratch them.We work on obsolete Studebaker and Packard engines for which parts are not always available. Another enthusiast designed an adapter to enable an Oldmobile V8 oil pump to be used on the Packard V8. However, he couldn't find anyone to do the manual machining consistently at an affordable cost. The tolerances were just too difficult to hold doing each setup by hand. He asked me to take over the project and I happened to know a talented CNC guy who had a one-man shop. Once this guy did the program, he can run off this complicated part at an affordable price and each piece is dead nuts, when the manual machinist just couldn't do it.jack vines