Mirror finish with HSS tool bits

T

taiwanluthiers

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Is this possible at all? I know the stuff about nose radius and all that, and grinding a proper tool bit. I followed it to the letter yet when I turn steel with it, the finish is at best a brushed finish, not the mirror finish that carbide inserts give if you follow its recommended cut. Or is the poor finish caused by the fact that the tool bit needs to be lapped and polished the same way carbide insert is done?

I tried stropping the edge on HSS to give it a fine grit edge, but it would still give a brushed finish, not a mirror finish.

What can we expect for finish on HSS tool bits?
 
benmychree said:
Mirror finish with HSS is very unlikely to happen, or with carbide either, that is what grinding, polishing and lapping is for.
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I don't know what you mean....

With carbide insert if you follow their recommended speed, depth of cut, etc. they give out shiny finish even on mild steel. Not exactly mirror but shiny.

The only finish I got out of HSS is dull, brushed finish.

My question is, is that expected?
 
Yes, expect it; cutting tools whatever they are made of give better finishes at higher surface speeds, HSS fails because it cannot be run at higher speeds that would give better finishes, true as opposed to ceramic, and other non metallic tools including diamond.
 
Mild steel usually "tears" somewhat when turned so I usually don't expect a super shiny finish unless I polish it later with emery cloth or something like that. You should be able to obtain a similar finish between the two different tools but probably not exactly the same for various reasons including sfm requirements (surface feet per minute)
 
Reflectivity may be misleading. Look at the surface with a 10x loupe. The sharp hss could be actually a smoother overall finish, but dull or matte looking. I’ve seen lots of carbide turned parts that are shiny but have a high degree of roughness due to the faster feed per revolution required to get the carbide to work. smooth in the groove but like a record overall. For gooey steel try and grind up a shear tool for finishing. They work really well.
 
OTmachine said:
20 RMS is about the best that one can expect from a lathe.
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Perhaps, but 125 or 63 would be more like it; 32 would take hand work including polishing. Wondering about my seemingl odd numbers? this is what I was raised on, drawings were generally specified that way, the worst possible finish was 500, then 250, 125, 63, 32, 16, and that was about as far as it went ---- inspection had the lie detector, (profilometer), the machinists had their fingernails.
 
benmychree said:
Perhaps, but 125 or 63 would be more like it; 32 would take hand work including polishing. Wondering about my seemingl odd numbers? this is what I was raised on, drawings were generally specified that way, the worst possible finish was 500, then 250, 125, 63, 32, 16, and that was about as far as it went ---- inspection had the lie detector, (profilometer), the machinists had their fingernails.
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My friend Alex(Apple engineer) will only use a laser,checking the finish on phones.
 
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