deep drilling

[ra_balke]

I have about 2000 hours on my old 12x36 Atlas lathe, and I have done a lot of advanced things. I have turned barrel blanks, cut threads, cut chambers, turned inside threads, reverse threads... I even lathe bored a Hollow base Prichet mould for my 40 cal muzzleloader.. But one thing I seem not able to do is drill a deep stright hole.

Can anyone tell me how !

What I am looking to do, is drill some mould cavities to make hollowpoints. How in the #@&%! Do I keep the bit running true and stright ?

Thanks

[trmungle]

Machine a bushing to fit inside the mold with the proper drill size hole in it. This will keep the drill from wandering and it will make a straight and concentric hole. Tom

[Buckshot]

..............ra_balke, I probably HP between 80 and 100 moulds a year for people. If you've done all that stuff I'm a bit surprised you're asking The first thing as you probably know is setup, and setup is everything and it's the only hard, or rather time consuming part.

.........



Once that's done I use a suitable OD centerdrill for a starter hole, and it's introduced just far enough to be just shy of the bit's OD.



Then you stick in the drill bit and let it do it's thang. Feed it no faster then it wants to cut. The only blocks I use fluid with is aluminum, and for that I just use WD40 (which is about all it's good for). Since the other blocks are cast iron or brass, they're drilled dry.



And the result.

..................Buckshot

[MtGun44]

Depending on how deep you mean. For a deep hole, like in a barrel,
you need a gun drill. We use these at work to make deep holes in
some classified parts, but we call them gun drills because the technology
is from making barrels.

The key difference is that a gun drill has a single cutting point, not two like an
ordinary twist drill. Here are the key points.

1 - no twist, single point cutting

2 - first roughly 1/2" to 1" depending in the hole diameter, is dead on the
desired hole diameter, the rest is maybe .005" or more undersized
3 - drill is hollow and lube/coolant is injected at the cutting face thru the
hollow bit
4 - the drill is a solid rod with the offset drilled hole in it for coolant and
a groove cut down the length. In cross section it has a "1/4 of the pie"
90 degree cutout - looks like a long straight slot in the drill.
5 - the single cutting edge has a point which is about 1/3 of the way from
the center of the drill and the edge of the drill.

6 - the drill has to be started with a hardened bushing to guide it straight
into the work piece since the body fit at the first part is what keeps it
straight.

Hope this helps.

Bill

[ARKANSAS PACKRAT]

MtGun44; The barrel drill machines in Bob Hoyt's barrel shop have hollow tubing bodies, not solid, and the workpiece spins, not the drill. It was explained to me that since the work spins, it tends to keep the bit on track. The smaller the hole, the faster it spins.
I have seen .500 holes drilled 34" into a .750 bar for musket liners.
This machine uses LOTS of cutting oil delivered at high pressure ,right to the lube hole in the cutting face. It makes LOTSA' oily chips in a hurry!
Nick

[ra_balke]

Well, thanks for the advice, but mostly I have tried that.

I set up in a 4 jaw chuck, I set the cavity to center with a dial indicator, I align the tail stock to the lathe bore, and I run the bit in,..... ( slowly ! ) from the cavity into the bottom, and invarabaly I get 1/32 of run out.

Maybe what I need is a new American made colbalt bit.

I do agree, wd-40 is good stuff for aluminum.

[R.M.]

Are you starting with a center-drill?

[Buckshot]

Well, thanks for the advice, but mostly I have tried that.

I set up in a 4 jaw chuck, I set the cavity to center with a dial indicator, I align the tail stock to the lathe bore, and I run the bit in,..... ( slowly ! ) from the cavity into the bottom, and invarabaly I get 1/32 of run out.

Maybe what I need is a new American made colbalt bit.

I do agree, wd-40 is good stuff for aluminum.

..............You don't need cobalt as you won't be generating any heat. Not drilling mould blocks anyway. You DO need a high quality bit though. One that cuts evenly on both edges, otherwise it WILL go off track. I really like namebrand 135* splitpoint parabolics for serious drilling. Doing these mould blocks I use surplus aviation 6" bits. Most are split points, most are M7 or M47 HSS, but all are high quality bits.

...............Buckshot

[JIMinPHX]

The gun drill is beyond what you need here, but it is the only way to go for Reeeeealy deep holes. I’ve managed to get 1/2" diameter cartridge heater holes drilled over a foot deep in 3/4" cold roll without going off center far enough to cause a problem, by using standard (long length) drill bits.

Pretty much everything posted above is good advice. I would add that you need to make sure your spot bit or center drill has sucked all the way into center & is giving you a dead center cone to start you regular bit in. Otherwise your bit will walk around.

A little background on drill bits -

Parabolic bits are sometimes called deep hole drills, even when they are “stub” or “screw machine” length which is quite short. The parabolics remove chips out of the hole better than standard bits do. The parabolic bits will require less backing off to clear chips.

135-degree split points are my general purpose favorites also, but any good quality bit in good condition will work fine here IF YOU USE A SPOT BIT FIRST. Brands like Clevland, Chicago-Latrobe, Precision Twist Drill, Walter, Triumph, Guhring, Keo, Titex, Atrax, Metal Removal & M.A Ford are examples of good quality bits. The gold colored stuff from Harbor Freight is not something that you want to use here. Those guys can’t even be trusted to get the drill point clearance angles correct, let along get both flutes symmetrical. Asymmetrical flutes will drill off-center & oversized holes.

Some people claim that the closer that you match the angle of you spot bit point to the angle of you drill bit point, the better it is likely to start. Others recommend a 90 degree spot bit for everything. Either way works fine for me.

Cobalt bits are actually a little bit softer than standard high speed bits of the same brand & quality. They are preferred in materials like stainless steel that produce a lot of heat because the cobalt alloys tend to be less heat sensitive. The truth of the matter is that you should be using lots of flood coolant when drilling high heat alloys like stainless regardless of what drill bit you choose. In these alloys, the split points really do help a lot more than an alloy change on the bit.

I will also second the motion about not using any lube when drilling cast Iron. If you do use lube, it will want to mix with the cast iron powder that forms, then turn to thick mud & jam up your bit. That's very bad juju.

When you drill aluminum, you want to use a bit with a more positive clearance angle if possible, but unless you are regrinding your own points, you usually just get stuck with whatever the standard offering is. I’m not talking about the point angle (118-135 degree) here. I’m talking about the point clearance angle (91-120 degree). That is the angle that you see when you look at a bit from the point end. You can’t see it on a split point bit. Stainless & aluminum like very positive clearance (closer to 120). Copper & it’s alloys like the angle very close to 90, so that the bit doesn’t dig in by itself. Other materials are somewhere in the middle. The closer to 120, the less force you need to drill with, but the more likely the bit is to lock up, especially as the point of the bit gets to the back side of the material at the end of a thru-hole.

Drills also need to be run at the right speeds. Rule of thumb is just under 500rpm for a 1/2" bit in mild steel with lube. As the bit gets smaller, you need to spin it faster to keep the surface speed of the outer flute the same. As the bit gets bigger, the speed gets similarly slower. Go faster for aluminum. Go a lot slower for stainless. Go pretty slow in cast iron & clear chips often.

Aircraft extension bits usually have only partially fluted bodies in front of their shanks & require frequent chip clearing when drilling deep holes. They also tend to have thick webs. This makes them a little extra rigid, which is a good thing, but it also takes away chip clearance, which is a bad thing & is another reason to clear chips frequently when using them. The thick web also makes them very hard to repoint well if you don’t have a point splitting fixture. There are other types of long bits, that have more standard web profiles, but they tend to be flimsy.

[blysmelter]

Does 1/32" rally matter?

[Buckshot]

Does 1/32" rally matter?

..............I dunno because "It Depends" . If I have a pile of 2x4's and 2x6's and I'm building a couple picnic tables and benches for me and the neighbor I watch ths 8th's and try to catch the 16th's, but 32nds are invisible.

If your boolit is .314" in OD and the one block is offset by a 32nd, will it matter? A 32nd is .031".

...............Buckshot