Rube Goldberg Tool Post
May 13th, 2009How Jeff Foxworthy Would Run a Lathe
I have an idea for making a base for my quick change tool post. The existing base is too wide. It’s a rectangular piece of metal about 3/8″ thick, maybe 2 1/2″ long, and 2″ wide. There is a rabbet (don’t know what else to call it) about 3/16″ deep down each long side. There is a 5/8″ bolt hole in the center.
I can replace this with a round base; rectangular is better, but round can be made to work. I’m thinking I might make one out of aluminum, since I have 2″ bars on hand.
Here’s the plan.
First–this is the part that will make everyone shriek–I’ll make a 5/8″ hole using a wood spade bit held in the tailstock.
Wait! It will work! I’m sure of it. I have no 5/8″ metal bits, and I’ve used spade bits in aluminum. If I go slow and use lots of WD40, it will work.
Okay, then I turn the bar down until it’s the same width as the tool post slot. Then I put a groove in it about 3/16″ wide, to simulate the rabbety thing in the existing base. Then I part the result off. I end up with a giant washer with a step in the side.
Crap, it has to be threaded on the inside. I’ll never be able to do that. Even if I could thread, the existing bolt is metric.
I guess I better go look at the parts again.
May 13th, 2009 at 12:24 PM
You can thread with these things called “taps”.
You don’t need a threading attachment on the lathe to use one! And they’re available in metric sizes!
May 13th, 2009 at 12:25 PM
If I’m going to start spending money on it, I might as well pay someone to machine the original part.
May 13th, 2009 at 1:28 PM
There is a reason why they make those things out of steel.
Using a spade drill might work, but I wouldn’t expect the hole to hold to the tolerance you need to tap a thread. If the hole looks like 5/8 to you and is metric, it is most like an M18. The tap drill is 15.5mm or .610 for that size. Your spade bit will drill oversize and you will have not much thread in a weak metal to hold your toolpost in place.
Putting aside the use of a round aluminum disc in place of a rectangular steel plate, you want to be really careful if you want to part off a 2″ disc. Parting off can be pretty tricky, and digging an inch deep into that aluminum could get very exciting if your parting tool is not super rigid and set perfectly. Exciting means things breaking. I recommend you use a bandsaw or hacksaw. Sawing is the fastest way to remove stock. If you are careful, you can hacksaw the disc off in the lathe by running at slow speed. Be careful.
In general, I think this is a bad idea. Pay someone to machine the existing plate to width, or else hacksaw and file it to fit.
May 13th, 2009 at 1:57 PM
Someone here will tap, or thread, it for you if you do everything else and send it to them.
I’m not volunteering till I know the tap size and whether I have one.
May 14th, 2009 at 8:55 AM
New betting pool: Number of days until the blog owner’s name changes to “Lefty.”
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“That Steve’s All-right with me.”
(disclaimer – I’m not a machinist.)
(Another disclaier – I once got bitten by a band-saw.)