Drilling bronze valve cages. Not happy

[bullpeters]

Trying to Make bronze valve cages. I only need two but have only managed one from four attempts. The holes won't stay centered!!
. I am drilling on the lathe, have done this in others metals without issue. Is it the bronze? Do I give up? Any tips?
Drilling 4mm guide hole and 8mm passage. Drilling undersized and then renaming. The 4mm hole goes crooked and that's that.

 

[sssfox]

Are you starting with a center drill?

 

[bullpeters]

Yes, lard for lubricant, and a sharp drill, pecking at it

 

[sssfox]

Do you have a different drill bit you could try?
It doesn't have to be 4mm.

 

[sssfox]

How deep are the holes?
Could you drill half way through, turn the piece over and drill the other half?

 

[enfieldbullet]

try a flat drill or a boring/facing bar, should work with less deflection.

your problem here is either deflection of the drill , drill wander (very likely with twist drills), or work moving around in the chuck.

try the flat drill, buy some HSS round stock 4mm and grind it to shape(some call this a 'D bit' because you grind half the diameter off ). almost like gundrilling.

you're right, must be the bronze 'grabbing' the drill and making it shift in the chuck or causing the drill to wander.

 

[Walltoddj]

You might want to try a brass grind on the drill a sharp drill bites in but with the cutting edge flat as for brass they don't dig in and tend to cut straighter. It's worth a try and you can always sharpen it when done or do like I do leave it for cutting brass, copper, and bronze.

Todd

 

[bullpeters]

Am going to sleep pondering a "d bit" or a "brass grind"!
4 mm boring bar would be the trick, but
Size, rigidity???
I like the idea of expanding my skills and have recently discovered drill rod. D bit seems at the front.
It's a thru hole maybe 20mm, to lazy at present to go out and check
Thanks

 

[bullpeters]

Forget drill rod comments, Sunday is a really long work day, 16 hours and I am going to sleep
Thankfully 16 hrs in front of people not machines
People bite but not as often or badly than machines when tired
Wives???

 

[kvom]

Drill with a 7mm and then ream. Thicker drill deflects less.

 

[BaronJ]

Drill with a 7mm and then ream. Thicker drill deflects less.

Yes I agree ! Its possible/probable that the drill is ground off centre. I've just had that problem drilling a 2.5 mm hole to put a M3 thread in mild steel, 8 mm deep. The hole is actually curved like a banana ! The drill looks fine until you put it under a measuring loupe. One edge is lower than the other. I don't have another drill that size and trying to regrind it, I just made it worse. :wall:

 

[Walltoddj]

Yes I agree ! Its possible/probable that the drill is ground off centre. I've just had that problem drilling a 2.5 mm hole to put a M3 thread in mild steel, 8 mm deep. The hole is actually curved like a banana ! The drill looks fine until you put it under a measuring loupe. One edge is lower than the other. I don't have another drill that size and trying to regrind it, I just made it worse. :wall:

That's one nice thing about the Drill Doctor it's quick and easy. I've always hand ground my drills that was the way I was taught and years of doing it but the Drill Doctor makes it very simple.

Todd

 

[abby]

You did not mention speed , some bronzes work harden very quickly if drilled or turned too fast , this will cause a drill to wander off centre.
A drill ground off centre will cut over size but should still follow a straight path.

 

[Hopper]

I was taught as a toolroom apprentice:
Drill to remove metal quick and rough.
Bore to get concentricity/location.
Ream to get final size and finish.

The only way to be sure to get a true concentric hole is to drill it undersized and then bore it.
You can bore it to a couple of thou under final size and put the finish on with a reamer. It will follow the concentric bored hole as long as you bore to say .002 under final size.

It's a bit time consuming, but you can make a nice small boring bar for small holes by grinding it out of solid square HSS toolbit blank. 5/16" works well for small jobs.

You grind the shank down from square to round, make it tapered from the full 5/16" at the one end down to about 1/8" on the front end. Leave the very front end unground so you can then form the cutting edge on it. The other end is left the original 5/16 square to grip in the toolpost.
(Bit hard to explain but I dont have a pic handy)

For something a bit bigger, like your 8mm hole, a 3/8" HSS blank may be better, but will take longer to grind to shap. But for 8mm you should be able to buy/make a conventional boring bar .

 

[purpleknif]

Try starting the hole with an end mill.

 

[Charles Lamont]

If it is drawn bronze it may be better annealed.

 

[BaronJ]

That's one nice thing about the Drill Doctor it's quick and easy. I've always hand ground my drills that was the way I was taught and years of doing it but the Drill Doctor makes it very simple.

Todd

Hi Todd,
I've been collecting bits for a while now in order to make a tool & cutter grinder. In fact tomorrow I'm going to weld the motor mounting plate to the base plate. I'm using a universal motor salvaged from an electric lawn mower. All of 1200 watts. I don't know what the speed is yet. I intend to make a speed controller for it. I should take some pics.

 

[enfieldbullet]

Hi Todd,
I've been collecting bits for a while now in order to make a tool & cutter grinder. In fact tomorrow I'm going to weld the motor mounting plate to the base plate. I'm using a universal motor salvaged from an electric lawn mower. All of 1200 watts. I don't know what the speed is yet. I intend to make a speed controller for it. I should take some pics.

those universal motors will get to 10krpm easily, maybe to fast for grinding. you would be better off with a house fan motor as far as speed goes. less chance of the grinding wheel exploding.

you don't really need much power in tool sharpening grinders, or speed for that matter. the speed control if done by a variac will reduce the motors power as well.

 

[GWRdriver]

Assuming this is for a steam engine, the valve "cage" is unfamiliar to me, could you please clarify? The two bits which most often need this treatment I know as the valve chest and the valve yoke. For those two I've never found a reliable way to do this in small sizes, the overhang is excessive, so I would center (Slocumbe) drill to depth, ream, and hope for the best. If the drilling face is milled flat and perpendicular drawn bronze should not need to be annealed.

 

[BaronJ]

those universal motors will get to 10krpm easily, maybe to fast for grinding. you would be better off with a house fan motor as far as speed goes. less chance of the grinding wheel exploding.

you don't really need much power in tool sharpening grinders, or speed for that matter. the speed control if done by a variac will reduce the motors power as well.

Hi, Thanks for your notes.

I agree about the speed. I did try the motor with no load, and it screamed like a banshee. Virtually no sparking from the comm, so it seems to be electrically in good condition. It has ball races at either end of the spindle without any detectable play.
I did try running it from a variac and the speed varied smoothly without any sudden jumps.

The grinding wheel that I propose to use is a 5" X 1/4" flat one that is rated for 5000 rpm. I have collected all the parts to build a triac speed controller, so I should be able to vary the speed from almost a standstill to its maximum. What did surprise me a little is that there is no fan to cool the motor. At the rated 1200 watts, nearly 2HP, I would have thought that a cooling fan would be mandatory.

I started welding the motor mounting plate to the baseplate today. I will have to take some pictures before I go any further.