Question About Hss Lathe Tools

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mzvarner

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So a little back story, because maybe its operator error and not the tooling (but that's never the case...right?)

I was using my little Central machinery 7x10 to bore out a 5/8" brass rod that is just over 9" long. ( I would indicate to 0, face/ bore half, flip it around, then indicate, and bore the other half). I started by facing the end I was going to work with. I started using some of the cemented tooling that i got with the lathe, but they were leaving an awful finish. I assume because they are not sharp. I switched to 3/8" index-able carbide and ramped up the RPM, and fed the tooling faster than usual, and it got better. I ground down the rake on the drill bit i was using (the best I can with the stones I have). However, I did this after I was done with the first half. I pulled the piece from the chuck and noticed the rod was now bent!!! That seems like a HUGE amount of force occurring in there. What did I do wrong?

Anyways my original question. When grinding tools for brass you want 0 top rake. Can I get away with just grinding one set of tools that are designed for brass turning, but still use them for steels and aluminum? I ask because I have limited space in my "shop".
 
Bending a 5/8" OD brass rod by just facing and boring takes a great deal of axial force if you're only working from the end. How are you holding the part - just the chuck, chuck plus a steady rest, face close to the chuck with most of the work through the spindle? Are you actually trying to bore a hole or are you trying to drill it? The processes are completely different. It would help us to help you if you show a pic or describe your set up more carefully.

Brazed carbide, provided it is reasonably sharp, will put a mirror finish on brass but the tip must be on center so check that. A diamond stone will easily sharpen these tools.

HSS tools for brass typically have zero top rake but 5 degrees of side rake with zero degrees of back rake works better. The rake angles for tools used on steel and aluminum differ greatly from tools used on brass but they will still work if the set up is rigid.

It is very likely that your results can be improved if you post a pic of how you're set up.
 
Yes. Drilling (not boring) a 4 1/2" deep hole sub 5/8" diameter.

The stock was mounted with out a steady rest. I had it chucked with an inch or two sticking out the rest through the spindle. I would not have had room to use a steady rest and drill that deep. I will try to get a pic later this afternoon.

Sorry for the miss use of terminology.

Sounds like it does matter about the angles. HSS blanks are cheap so I should just have a few here. Now I just need to get setup to grind them. Have a 6 inch grinder but just not the right wheels yet.
 
Don't apologize. This machining stuff can be difficult in the beginning, both to do and describe. Yes, a pic would help. Try to include the entire set up as it was when you were working. If you will, tell us what you're trying to make.

It is going to be a challenge to drill a 9" long piece of brass from both ends and have the holes align. Moreover, a typical jobber drill will not go 4-1/2" deep so you'll need an extra-long drill. Anyway, give us more details and we'll see if we can help you sort it out.
 
Is the od 5/8" dia.? What size drill are you using?
 
So the brass rod was actually 1/2 inch. I was drilling with a 3/8" (I think I see a problem?). All I did was center drill, I did not step up in drill sizes. None of my drill bits are that long so I figured that at some point I am going to be drilling the full 3/8 so might as well just go for it.

Here is what the setup looked like...

thumbnail_IMG_0183.jpg
 
Your set up looks good - short overhang of the work and you did not pilot drill so the drill should go in pretty straight, assuming the drill is ground correctly. I am not clear how the bar bent since all the force is axial. Maybe someone else has a clue?

Is it necessary to use solid stock? You can buy brass tube with approximately a 1/16" wall. Is this a special application?
 
Is your tool bit on center?
Is there enough clearance so the bit isn't rubbing in the bore?
Is your drill bit properly sharpened?
How much knocking around does it take to indicate the rod in? Are you sure the end in the spindle is running true?

You COULD be generating enough heat by drilling and being a pretty thin wall the heat could soften up the brass enough where the weighted back end whip is causing the drilled out area to bend. Try a smaller drill bit before drilling with the larger drill bit. Try having more stick out of the chuck. If you don't have to knock it around too much to indicate it in, try drilling both sides out with the smaller dia. drill bit then the larger bit. I have seen some pretty small dia. boring bars so boring can be done in one shot through.
 
No it is not necessary to use solid stock. I was just trying to use what I had on hand. I am going to buy brass tubing now.

I think heat may have been the problem. The very top where the drill enters developed a light red sheen to it. I also think that I need to recheck my tail stock center now that I think of it, because the bit did wonder a little even after center drilling.
 
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