Trying To Cut A Groove And I'm Stumped

steve45 · Aug 31, 2016

I'm trying to cut a .100" wide groove in a 3/8" bronze shaft. I have a 1/8" wide HSS parting blade and ground it to a thickness of .100".

Problem is my groove comes out about .097". I've measured the width of the blade with two electronic calipers and a micrometer. They all show a thickness of .100" +/- .005. I've check the calipers and mic with a .100" gauge block and they're within .0005.

After I cut the groove, I tried to stick the gauge block in it and it won't fit, so the groove is definitely less than the desired size.

I'm pulling my hair out! I have measured and measured and come up with the same answer each time. How in the world am I cutting a groove that's smaller than the bit???

yardbird · Aug 31, 2016

It's cocked at an angle would be my first guess. Run a indicator across the tool holder see if it's setting flat?

You could take two stabs at it to widen it up?

Brent

CarbideBob · Aug 31, 2016

Can we assume your wall finish on the groove is 6rms or better?
No visible feed lines that would screw up an min/max cut measurement?
Bob

AlfredLyon · Aug 31, 2016

Bronze can be very "gummy". If you dont have side relief on your cutter faces, front and back, the material can actually spring back slightly at the top of groove.

Alfred

Onepass · Aug 31, 2016

Yup. It's bronze. Ever tried to drill and or tap bronze? With some alloys, you need oversized taps, drills start squeaking and get real hot!

L Vanice · Aug 31, 2016

steve45 said:
I'm trying to cut a .100" wide groove in a 3/8" bronze shaft. I have a 1/8" wide HSS parting blade and ground it to a thickness of .100".

Problem is my groove comes out about .097". I've measured the width of the blade with two electronic calipers and a micrometer. They all show a thickness of .100" +/- .005. I've check the calipers and mic with a .100" gauge block and they're within .0005.

After I cut the groove, I tried to stick the gauge block in it and it won't fit, so the groove is definitely less than the desired size.

I'm pulling my hair out! I have measured and measured and come up with the same answer each time. How in the world am I cutting a groove that's smaller than the bit???

They all show a thickness of .100" +/- .005" means the blade is between .095" and .105" thick. I guess a blade in that range could cut a .097" groove.

Larry

steve45 · Sep 1, 2016

Onepass said:
Yup. It's bronze. Ever tried to drill and or tap bronze? With some alloys, you need oversized taps, drills start squeaking and get real hot!

You're right about that! This is a fuel line fitting and when I drilled & reamed a 1/8" hole through it, it turned blue.

I'll try adding some relief to the cutter.

Thanks!

Onepass · Sep 1, 2016

steve45 said:
You're right about that! This is a fuel line fitting and when I drilled & reamed a 1/8" hole through it, it turned blue.

I'll try adding some relief to the cutter.

Thanks!

If this is an ongoing project, different alloys of bronze have different responses to cutting tools. It's been a while and I don't remember the specifics, but if you can vary the material type, I'm sure you could research which alloy might be better for you !

Mtndew · Sep 1, 2016

What type of bronze? Ampco 18, 660? Big difference between how those two cut.
One is a mofo the other is like butter.

Johnny Larue · Sep 1, 2016

steve45 said:
You're right about that! This is a fuel line fitting and when I drilled & reamed a 1/8" hole through it, it turned blue.

I'll try adding some relief to the cutter.

Thanks!

tip...when ever it turns blue...or your size is under sized like the problem you have...its speed...too fast...slow it down...and cool it more....the hole will be larger and so will the slot...try it....bring speed way down...so only nice brass colored chips and part is not hot....then like your .003 under...then you can take .0015 per side on a second cut WITHOUT that speed heating everything up and SCRAPPING THE GROOVE since the heat enlarged everything...good luck....also more of angle on cutting surfaces produces less heat and closer tolerance....the old way was to take off the sharp edge and rub brass so it don't grab....but in this instance you need sharper so the tools wall does not produce heat....heat is your problem here IMO.

jscpm · Sep 2, 2016

Don't try to cut to better than 5 thousandths, especially in springy metals like cold rolled or bronze. Just the strain relief alone is going to affect the results. Whenever you machine anything with latent stress, it is two-step operation with a seasoning period of several weeks in between. This can be avoided by fully annealing the metal.

Bronze can be annealed by first melting borax at 1400F, dipping the part in the borax, then hold the part at 1350F until is soaked through. The part is then plunged in water. If you perform this operation without using the borax, the surface of the bronze will be oxidized.

To harden bronze, repeat the same process, but allow it to slowly air cool in the furnace, do not quench.

To create something like a precision groove, I would first polish the bronze, then anneal it, then scrub off the flux, then cut the groove slightly undersize, as though for reaming. Then I would use a copper lap to lap the groove to size. Finally I would harden the bronze, scrub off the flux and polish.

steve45 · Sep 2, 2016

L Vanice said:
They all show a thickness of .100" +/- .005" means the blade is between .095" and .105" thick. I guess a blade in that range could cut a .097" groove.

Larry

Sorry, typo. It should have said .100" +/- .0005".

steve45 · Sep 2, 2016

Mtndew said:
What type of bronze? Ampco 18, 660? Big difference between how those two cut.
One is a mofo the other is like butter.

Silicon bronze, C655.

Johnny, I'll try cutting slower. Seems reasonable to me.

jscpm, Wow! I didn't think this would turn into such a project! I appreciate your input!

HuFlungDung · Sep 2, 2016

steve45 said:
I'm trying to cut a .100" wide groove in a 3/8" bronze shaft. I have a 1/8" wide HSS parting blade and ground it to a thickness of .100".

Problem is my groove comes out about .097". I've measured the width of the blade with two electronic calipers and a micrometer. They all show a thickness of .100" +/- .005. I've check the calipers and mic with a .100" gauge block and they're within .0005.

After I cut the groove, I tried to stick the gauge block in it and it won't fit, so the groove is definitely less than the desired size.

I'm pulling my hair out! I have measured and measured and come up with the same answer each time. How in the world am I cutting a groove that's smaller than the bit???

Your cutter is not as sharp as you think it is. It needs to be widest at the front, without question. A parallel sided tool is difficult to figure on where the true width measurement is coming from, so you deliberately give it relief on both sides so that the front has to be where it is widest. The corners need to be truly sharp, no round over, as viewed under a good magnifier. This is easiest to accomplish if every face of the tool is ground as one facet with a flat faced wheel. It can also be 'hollow ground' no problem, but it must not be convex ground on any face.

I'd use carbide for grooving Ampco aluminum bronze metals, but regular brass or bronze is easy to machine with a neutral rake HSS or carbide. Very sharp is key, as some guys would say, the tool must never have cut any steel since it was sharpened or it is likely not suitable for machining brass or bronze.

Mike C. · Sep 3, 2016

For a really precise groove, I'd make it a two pass operation with a narrower blade and a DI on the lathe bed. Plunge a .070 or so thick groove, then step over and finish it to full width. Unless it is a deep groove, the tool should be stiff enough to resist flexing on that light a cut. As said before, SUPER sharp tooling. Hu is dead on, not a lot of rake needed, but it has to be razor sharp.

bustamallard · Oct 11, 2016

AlfredLyon said:
Bronze can be very "gummy". If you dont have side relief on your cutter faces, front and back, the material can actually spring back slightly at the top of groove.

Alfred

I have seen that with copper alloys. Especially BeCu. Stuff grows. I would consider adding a small shim to make blade wobble. Might take some guesswork.

SJH1057 · Oct 11, 2016

Check your tool center height.you may be above center

Jim Williams · Oct 12, 2016

I think Mike C. has the best answer. If I were cutting the groove, I would use the tool you have, and then move the carriage an appropriate amount to widen the groove. I have a micrometer carriage stop for my lathe, which I have found useful for a number of operations.

Jim

onecut · Oct 12, 2016

Obviously must be a decent grade of material.Put a bit more effort into sharpening your tool and hone it-Can be horrible stuff to machine.What a cutter mics at and what it cuts at is a different thing,otherwise I would never get a keyway right on my manual mill I always use a new tool on stainless keyways knowing its going to cut tight to the mic size-If I used a dead size cutter it would always cut minus,put a bit of mild steel in and see the difference-Not too many revs either might have been usefull if you stated the material grade.Some will machine without problems whilst others will squeal and crunch its way thro.Maybe your tool is pushing down a few thou,could be worth trying it a few thou above the C/L.I agree with whats been said regarding opening the gap out with a second pass if its a good material it will be a pain far better using a smaller tool then open it up-Equal ammounts off both walls

gwilson · Oct 12, 2016

If it's only a thou or so under size,can you take a needle file,or even an 8" mill file(grind the end off till teeth go clear to the end),and file the groove a little?Keep checking the groove till you can insert the gage block. No need to get complicated.

Some bronzes,as stated,can be very tough to cut.(I know,having made 2 large cannon from Naval bronze!)

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