How to converge to the desired diameter when fitting pieces?

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whateg0
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Re: How to converge to the desired diameter when fitting pieces?

Post by whateg0 »

It's been my experience that carbide inserts do not sneak up on a dimension as well as hss, at least not out of the box. Of course, grinding your inserts defeats the purpose of using them in the first place. As mentioned early on, it's usually better not to sneak up on it.

I have probably read the linked thread before but I'm not doing it now, so this might be redundant. Turn down to a diameter a bit bigger than the final dimension. Then take approximately half of that in a single pass so you can measure to see how much it actually took. Depending on chip load and tool shape, you will often find that it took more or less than dialed in. How much it took off is less important than how much is left though. Because you took half the next pass should be pretty similar in how it cuts so you can dial in whatever is left and should come out awfully close, though I often still do shoot for about 5-10 tenths over so I can polish it.
RSG
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Re: How to converge to the desired diameter when fitting pieces?

Post by RSG »

dml66 wrote: Mon Jul 04, 2022 8:46 am I was machining a piece of 12L14 steel.
I don't have much experience with it but from the little use I've had it gave a better finish then the more common 1018 I have available to me. I prefer to use HHS that I grind (As Glenn mentioned) which can provide a better finish and enable you to take lighter, cleaner cuts. That way you have control of the profile of the tool as well. I'd suggest you move that thought up on learning how to grind your own tooling sooner than later. You'll wish you did years ago. There's a whole thread on it posted by Harold some years ago that is full of good info.
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pat1027
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Re: How to converge to the desired diameter when fitting pieces?

Post by pat1027 »

dml66 wrote: Mon Jul 04, 2022 11:39 amI've yet to grind my own tools, it's on my list of things to learn.
I went down a similar path. Machining being a hobby I wanted to spend time on making parts vs. learning to grind tools. Inserts seemed the way to go. Results were mixed. Light cuts were often inconsistent taking almost nothing off or more than I'd moved the tool.

Going back to HSS tools I watched this video https://youtu.be/__A2xtLF0AU and said "Is it that easy?". I ground a similar tool, made a few cuts that went way better than the insert tools.
Santafescotty60
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Re: How to converge to the desired diameter when fitting pieces?

Post by Santafescotty60 »

Are you using telescoping gauges and a micrometer do you have a DRO on the lathe to measure the bore, if you must buy a brake cylinder hone and polish it up. once your close Cheers Scotty
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liveaboard
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Re: How to converge to the desired diameter when fitting pieces?

Post by liveaboard »

I use emery cloth wrapped around a dowel to polish small bores.
Glenn Brooks
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Re: How to converge to the desired diameter when fitting pieces?

Post by Glenn Brooks »

What grade emery cloth for polishing?
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liveaboard
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Re: How to converge to the desired diameter when fitting pieces?

Post by liveaboard »

120 works well; finer than that gets clogged up pretty quick.
I have a lot of 180 and I'm not happy with it.
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Bill Shields
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Re: How to converge to the desired diameter when fitting pieces?

Post by Bill Shields »

Finer -> with a bit of water -> keeps it clear
Too many things going on to bother listing them.
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Harold_V
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Re: How to converge to the desired diameter when fitting pieces?

Post by Harold_V »

Bill Shields wrote: Sat Dec 24, 2022 2:18 pm Finer -> with a bit of water -> keeps it clear
Not all abrasive cloth/paper found in the shop has waterproof adhesive in its makeup. Water is also not an acceptable fluid on machine tools unless you don't object to rust.

Solvent (mineral spirits, Stoddard solvent, paint thinner) serves perfectly well.

H
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liveaboard
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Re: How to converge to the desired diameter when fitting pieces?

Post by liveaboard »

I'll give it a try; but that's pretty volatile stuff.
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Harold_V
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Re: How to converge to the desired diameter when fitting pieces?

Post by Harold_V »

I'm 83 and have never had even one questionable issue by using solvent. Been using it since I first worked in the shop, beginning in '57. While it burns, it isn't easy to ignite. Safe enough to be used and won't cause failure of the abrasive medium. Even waterproof types aren't as robust once wetted by water.

If you're really uncomfortable with the idea of using solvent, try using a light oil instead. Anything that will lubricate and flush the abrasive is helpful.

H
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Rwilliams
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Re: How to converge to the desired diameter when fitting pieces?

Post by Rwilliams »

Try coating the surface to be finished with black Sharpie pen. Make sure the surface is free of all oil to begin with using something like Acetone. Once the black Sharpie ink dries, use a wide piece of Aluminum flat stock to press some 320 grit wet dry automotive sand paper against the rotating part. This will quickly show any high spots. Add some WD-40 to the surface and keep the abrasive moving as the black low spots become smaller and smaller. Soon the part will be nice and smooth. Black Sharpie marks are great for letting one know where any low spots are. Quicker and faster than layout dye.
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