Homemade Lathe Part 10

Homemade Lathe Part 10

Learning - Using & Modifications

This is the last day of a 6 week stretch of -20C or colder, with only 2 days above -15C. I caught this image on Wed Feb19th on the way to work in the A.M. right out the window of the truck.

What does this have to do with the Lathe or even metal casting? Everything, in that I can't/won't melt metal under -15C, and I can't get the workshop.ca warm enough to work.

So this week as we've had 36hrs of non-stop snow up from the US North East coast, I finally had a chance to get back to the lathe.

This is a 5 Gallon bucket almost full of Alum ready to be cast. Over the last few weeks I've taken to melting over-sized chunks of transmission and other scrap in the wood furnace (like the shop heat furnace), with very good results.

I don't have enough heat to melt in a crucible to pour/cast. Also in the pile is a full metal cased Circ Saw and a few hard disks and other misc electronics scrap. and sprues and feeds going back to Dec.

There have been a few modifications to the lathe as I've been learning how to use it. Mostly what I've been trying to learn is the limits of the lathe and how to keep it just before the point of "Chatter".

Initially I thought it was normal to have the bit screaming and everything shaking. As I really value my hearing, I'd taken to wearing hearing protection. But after corresponding with a number of individuals via Email, I was set on the right path. To that end I had a chum up for an afternoon to give the unit the once over.

As often as I re-read saved Emails, all of the theory was put into complete context when watching someone actually run the machine. The sound of the cutter in tune, and the angles of the bit were memorized and will follow me to the grave. In fact I'm glad that no one ever saw me standing in front of the machine with a shit-eating grin as I'd feed the bit in to the point that the machine would virtually be ripping itself to pieces.

Now that that unpleasantness is behind us, here are the mods. The Cross-Slide was a spot that I kept adjusting, until I finally added 2 more gib adjustment screws.

This was done just this weekend. Prior to that I did totally disassemble from the saddle to the toolpost and shimmed and filed until everything was completely without slop.

The first 2 screws were positioned such that a 1/32nd of side to side movement would start after about 1/2hrs light work or sooner. Once the additional screws were drilled, tapped and adjusted, I ran the lathe for a few hours and they still don't need to be touched.

The tool post has had a few more mounting holes drilled to allow more angles of movement. And I'm getting a better sense of the T-Slots and how to position the post on them.

This post was fashioned in a pinch when the original casting came out malformed due to the cold in early January. Though it does seem sturdy I think it could be substantially improved by a beefier 1/4" base and deeper penetrating welds to make it all a bit more rigid.

The current base is 1/8" plate and warped slightly when originally welded.

The image to the right shows a betting view of cutting bit mounted in the post.

Of the numerous rookie errors, I had the bit extended too far out past the post and it had a levering effect on the entire assembly.

The other issue that (I'm proud to have found myself) is the bit wasn't at the center of the spindle. Though off by only a small amount (possibly 2 - 3degrees) the flat profile of the bit and degraded "Back Rake" or "Relief angle" contributed to the digging in action of the bit.

What clued me in was that with a #16 pitch, I have 1/64" feed with a 1/4 turn of either handle. But if the bit ever stopped the work, I'd have to really crank (backward) to disengage the bit.

The bit is angled down to achieve centre and also to get a better cutting angle. The shim is a small chunk of cast Alum that I filed to shape.

The cross-slide lead screw is better illustrated here. This is a good example of a minor mistake having significant implications. I couldn't wait to cast the actual slide assembly, so I drilled and tapped the saddle right on the bed.

The hole is not only on an angle, but it creates an issue with the cross-slide needing an oversized hole. A large washer at the front and the locked nut at the back seem to pick-up any slack though.

Cleaning and oiling obviously has an impact on the overall feel of the machine, a white handle from an old paint brush is visible on the table that I use to brush down things when need be.

So as another week threatens to start in a few hours, files will get saved and posted and the idea factory shutdown till next Friday afternoon, just a little after 4:00P.M.

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