Drilling longish holes

[max corrigan]

A simple question to the machinists among us! what is the correct way to drill (bore)a hole through bronze the hole to be drilled would be roughly 3/8" the length of the hole around 3" i know you would face of each end and centre drill,and then go up from a pilot drill etc. i have drilled longish holes in the past but when the drill comes out the other end it is often off centre
would you start drilling from both ends? then at least you would have two central holes but probably have a bend in the middle as each drill would follow the pilot holes
Also would you put the drill in the tailstock chuck and revolve the job, or visa versa
sorry for these newby type questions but i am not a machinist, so have not been taught the correct approach
Max.......
I hope i got this query in the right section, and not in the general section, please move if need be!

 

[rleete]

The "correct" method? I sure don't know. ;D

My method is to drill from both sides (double scotch yoke engine), and have them meet in the middle. Then ream, using a straight chucking reamer to remove the ridge in the middle. It wouldn't do well as a piston bore due to misalignment, but it apparently serves well as a bore for the valve. This was a long hole (4" IIRC), and about 3/16" diameter. The valve - 3/16" drill rod - seems to slide okay after a bit of lapping.

I'm sure one of the more experienced members will be along shortly to tell me how bass-ackwards my method is.

 

[Maryak]

Max,

This is the way I would do it.

1. A correctly sharpened drill is essential. One with the correct cutting angle and equal lengths on each flute. For bronze brass and copper, lightly stone the cutting edge to give a small amount of -tve rake.

2. In a home shop the lathe is usually more rigid than the drilling machine, so where possible spin the work and hold the drill in the tailstock. (There are many long write ups about the differing effects of work spinning v drill spinning on the drill and the hole being drilled).

3. Centre drill, preferably with a centre drill where the straight part of the drill is bigger than the centre of the actual drill for the hole.

4. Do Not drill a pilot hole. Small drills are far less rigid and are more likely to wander off centre. The deeper the hole the bigger the eccentricity.

5. Place a block of metal in the tool post square to the barrel of the drill and feed in until it just touches the barrel to act as a guide and stop the drill bending.

6. Start drilling and remember to clear the drill flutes and hole at least every drill diax3 depth of cut.

Goo Luck and I hope this helps. ???

Best Regards
Bob

 

[max corrigan]

Thanks Bob i will give that a go, i would have put a small pilot hole through first and then come unstuck! i will let you know how i get on and what it's for
Max...........

 

[Jasonb]

Bronze is always best drilled without a pilot drill as it can tend to grab the larger sized drill, plenty of cutting fluid will also help. I always used to drill bronze dry until I was told recently to use cutting fluid, it makes a lot of difference.

On very long holes another method is to center drill both sides, mount the work between a center in the tailstock and the drill in the head end, holding the work in a vertical slide or bolted to the cross slide. I recently drilled a 1/4" hole through 9" of cast iron this way going in from both sides and it was spot on.

Jason

 

[mklotz]

Bob's advice to use a correctly sharpened (new is best) drill is golden.

I would add only one small suggestion. Drill the first 0.5" or so of the hole undersized and then bore it out to the size of the final drill. This will act as a very effective guide for your new drill to follow.

Clear chips every drill diameter of depth as you drill.

 

[max corrigan]

This was the reason for drilling longish holes, this is my version of converting hand drill stand to tapping rig, thought i might share it with you folks

 

[compound driver 2]

Go With Jasons method but finish off boring between centers the last 5 to 10 thou.
What ever you do on bronze dont use a pilot drill youl pull the work out of the chuck. If you find its getting hot run the suds pump but over the work and not into the bore.
id look to using a 118 degree drill bit with relief notches in the cutting edges, this should break the chips a bit smaller and let them clear faster.
A little sandwich grease on the drill bity helps

The worst one iv done was 14 inches in PB109 on a 2 inch bore. I exeted to 5 thou of teh mark.

 

[SignalFailure]

My method is to drill from both sides (double scotch yoke engine), and have them meet in the middle. Then ream, using a straight chucking reamer to remove the ridge in the middle. It wouldn't do well as a piston bore due to misalignment, but it apparently serves well as a bore for the valve. This was a long hole (4" IIRC), and about 3/16" diameter. The valve - 3/16" drill rod - seems to slide okay after a bit of lapping.

When I built Double Scotch this bit gave me a real head-ache. In the end I drilled a 6mm (1/4") hole using a long-series drill bit and fitted a brass tube for the bore. You can see it on the first two photos on this page... http://sites.google.com/site/collectedinterests/model-engineering/engines/double-scotch

I was using steel rather than aluminium and found that drilling in tiny increments and clearing away the swarf every couple of seconds was the most accurate method.

 

[shred]

This was the reason for drilling longish holes, this is my version of converting hand drill stand to tapping rig, thought i might share it with you folks

cool idea. I have a Dremel drill-press stand moldering away somewhere that could be converted..

 

[rleete]

When I built Double Scotch this bit gave me a real head-ache. In the end I drilled a 6mm (1/4") hole using a long-series drill bit and fitted a brass tube for the bore. You can see it on the first two photos on this page... http://sites.google.com/site/collectedinterests/model-engineering/engines/double-scotch

Ah yes, I remember seeing that page. I found it when looking for solutions to my problem. I also had problems with the valve (major leaking), and I just couldn't get a good fit. My solution (not yet completed) was to take your brass tube idea, and modify it. I used 2 shorter tubes, one from each end. I then made the valve discs to fit individually, and lapped to fit. I made the center of the valve rod thinner to avoid any binding (bore is not perfectly straight through), and it seems to work. Since I didn't have a mill at the time, I couldn't easily make the yokes, and so moved on to a simpler engine for my first one.

 

[max corrigan]

cool idea. I have a Dremel drill-press stand moldering away somewhere that could be converted..

Shred go for it, the bronze i have used is way over the top! you could probably use almost anything even PTFE or maybe hard wood, but i had a piece roughly the size so i used that, the chuck spindle is from a printer nice and straight, could have been a bit a bit heavier but i don't intend using the setup for more than 4BA anything heavier i would do in the lathe
If i had bought the necessary materials to build from scratch ie MS Box section, steel plate or whatever for base etc. it would have cost more than the drill stand, so drill stand it was
Max.............

 

[SignalFailure]

Since I didn't have a mill at the time, I couldn't easily make the yokes, and so moved on to a simpler engine for my first one.

Hehe, I still don't have a milling machine. Turning square in the 4 jaw, drilling and filing was/is the order of the day!