HF 7 x 10 Mini lathe fun

cavecentral said:

Graphite is messy. I lay craft paper down to catch most of it, and use a piece to shield the spray of powder and direct it down into the catch below. Get 95% of it without a vacuum. Going slower helps too.

The bit does seem to gring more than cut, but it still works. That is why they do not need to me sharp. My tools for entrance and exit cones are wood spade bits ground to the proper angles. Don't need to be sharp, but you must grind the edge to 45 degrees to reduce friction.

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You might find this download useful. https://www.scribd.com/doc/17390328/Introduction-to-Lathe-Operations

Machining is all abour speeds, feeds, angles and fixturing. You need to learn how each tool removes material and set it up properly.

Tools have to be sharp or they will heat up the work piece, but they are not sharpened like a knife. A good lathe tool is kept sharp with a diamond sharpening stone. They work on HHS or carbide equally well.

If you run the lathe at too high a speed, or try to cut with a dull tool, both the tool and the workpiece will get hot. The workpiece will expand with the heat, and will be too small after it cools. The tool will get dull and possibly break, or break the workpiece. A lubricant, which can be any oil in a pinch will keep the tool sharp and cool and produce a smoother surface.

You can machine SS with HHS or carbide equally well, but you can run the lathe faster with carbide. I actually get a better finish when facing SS with a 1/4" bullnose HHS tool than wiht carbide, but you have to run the lathe at about 1/2 the speed.

Heat is carried away in the chips so you have to make a cut that is deep enough to make a reasonable chip, but not so deep that the lathe is working too hard. It usually better to take a shallower cut at a slight higher speed than to take a too deep cut at a low speed as that's how you can break the tool.

Another suggestion is to go to your local vocational high school and find out what text book they use in their shop course and buy one. You'll find it invaluable.

Bob

Thanks for the tips!

Machinery's Handbook is another good resource. It's a sort of one stop shop for information on everything from machining to bearings to threading to time value of money calculations. It's a bit pricey though; the current edition cost me about $80.

It is also worth noting that the cutting speeds, feed rates, depth, and tool angles listed in the machinists guide are to achieve maximum throughput in a production environment with production equipment. They are often not appropriate for hobby lathes. The OPs desire to turn a 3" piece of aluminum in a 7x10 lathe is an extreme example of this. And even with the "proper" equipment they are merely a starting point. There is no substitute for experimentation, practice, and experience.

There is a *huge* wealth of knowledge on you-tube, and you should check out this guy in particular if you haven't already found him:

https://www.youtube.com/user/mrpete222

I started on the same 7x10 lathe that you have. Turning anything 3" was very time consuming. I also found that concaved parting tools make great o-ring groove cutters. They really work better than the flat ones. Now I turn almost everything (except stainless) with carbide tools. I got a set of carbide insert grooving tools for o-rings and it is a breeze now. Same goes for threading - all carbide insert and they stay sharp and make cutting so much easier. For snap rings I found this great company that makes very reasonable and custom grooving tools for a very fair price (https://www.expresscuttingtools.com/)

Edward

Thanks for the link, I'll check them out. I use a flat parting tool for O ring grooves. Just need multiple thicknesses.

Finished my first nozzle carrier this weekend. Took about 10 hours total (I would starve as a machinist). Produced nearly a 5 gal bucket of turnings.

What did you start with to generate 5 gallons of turnings? At some point it pays to buy tube that you can machine the OD and ID on it. When I made a 6" nozzle carrier I bought a piece of 5.5" OD x 3.5" ID tubing and turned that down. Very little on the OD (.015") and none on the ID. Just had to made some o-ring grooves.

Edward

3" round rod. Bored out a 2" hold 2" deep. for the graphite with 1.5" Exit hole.

When I have done 75mm nozzle carriers before I've found that if I taper the insert and the nozzle you don't have to have a snap ring to hold everything in and they are faster to make. You still need to include a couple o-ring grooves for sealing, but the whole insert bears the load instead of a lip.

Edward

You still need the case snap ring to hold the carrier, right?

The end of mine is just nor bored out as much, forming a lip for the nozzle to rest on. With the pipe, I see where a 2nd snap ring would be used / avoided using your taper technique.

Yes, you still need the case snap ring. You don't need the carrier one and it allows you to have a bigger expansion cone.

Edward

Cool. I'll be using short cases (I'm level 2) so I'm not too worried that I'll need the extra room for a larger cone.