long through hole

J

jonathan01

Active User
Registered
Hello, I need to drill a 3/8" hole through the middle of a 9" long 2" dia bar. I will be using a lathe to drill the hole. I need the hole to be pretty straight. I plan on center drilling a hole, than use a screw machine length drill, than a jobber, than the extra long drill.

How straight of a hole could I drill?

Thanks
 
jonathan01 said:
Hello, I need to drill a 3/8" hole through the middle of a 9" long 2" dia bar. I will be using a lathe to drill the hole. I need the hole to be pretty straight. I plan on center drilling a hole, than use a screw machine length drill, than a jobber, than the extra long drill.

How straight of a hole could I drill?

Thanks
Click to expand...

Start from one end, drill half way through , flip part and drill half way through from the other end to meet in the middle. If you cant flip the part then the way you have it planned would be the way to go..

How straight the hole is will depend on how well the part is indicated, how well the drills are sharpened and on center, and also how true your lathe is..

If your tailstock is out say .001, by the time the drill travels over 9" the hole could be out quite a bit, but many other factors are involved..
 
What material?

I've had situations with longer holes but not quite as long as this. I view it the other way around. Make a bar around the outside of a hole; meaning, drill the hole then, put a supporting rod through the hole and surface the outside of the stock. The outside will be concentric -but of course, the hole may wander/neander a bit. I think how I know I'd address that but haven't really confirmed my thoughts.


Ray

jonathan01 said:
Hello, I need to drill a 3/8" hole through the middle of a 9" long 2" dia bar. I will be using a lathe to drill the hole. I need the hole to be pretty straight. I plan on center drilling a hole, than use a screw machine length drill, than a jobber, than the extra long drill.

How straight of a hole could I drill?

Thanks
Click to expand...
 
It will probably be 416 stainless.

I can flip the part. If I drill half and flip, as long as it is centered good, they should meet prefect, right?

That is a good idea about making the bar around the hole. That most important part of this is to have the hole straight. If I get a straight hole, than I can turn the outside down between centers.

Thanks, I think I may try drilling from both ends, than turn between centers.
 
Think it over and do some practice pieces -maybe on aluminum first.

Good luck w/416. Do you have a coolant drill bit?



Ray

jonathan01 said:
It will probably be 416 stainless.

I can flip the part. If I drill half and flip, as long as it is centered good, they should meet prefect, right?

That is a good idea about making the bar around the hole. That most important part of this is to have the hole straight. If I get a straight hole, than I can turn the outside down between centers.

Thanks, I think I may try drilling from both ends, than turn between centers.
Click to expand...
 
Ray C said:
Think it over and do some practice pieces -maybe on aluminum first.

Good luck w/416. Do you have a coolant drill bit?



Ray
Click to expand...


I am not sure about using 416 or not yet, i am leaning toward a SS, but may go with some type of regular steel.

I do not have a coolant drill. I have flood coolant, I think I am going to have to keep peck drilling it, and letting it cool.

I have a 135 split point drill that I plan to use. For the straighest hole, is it best to step up, say 1/8" to 1/4" than to the final 3/8"?

Thanks for all the help so far, I do plan on testing the hole in AL first.
 
I'm a little out of my league with this particular task and I'll gladly stand corrected but, I have some thoughts.

I don't think a 1/8 or 1/4" bit stands a chance of going through 9" of stainless (of any sort). Aluminum is challenging too because it packs-up easily. There's not enough chip clearance and not enough brute strength in the shaft. In the commercial world, this is probably done with custom carbide bits with high pressure coolant. 3/8" is the smalles size I think you can do this in a home shop.

Flipping a piece and getting the holes to match up will take a lot of skill and proper setup (which is exactly what another fellow mentioned) -and I'll bet dollars to donuts in a home shop environment, you'll still be off 1/8" in the middle. Also, when you're done with this, the hole will not be uniform diameter nor smooth -not by a long shot.

I'm not trying to dissuade you but, I don't know your requirements on this and want to give a heads-up.

I've often thought that if I find myself in this position, I would make a bearing mechanism that supports the drill shaft as it goes deeper into the stock. The drill bit itself would be very short in length and would be be spun on a long bar (smaller in diameter than the hole being drilled) with some sort of specialized chuck to hold the bit on the end. That's my uneducated guesss on how I'd tackle this.


Ray



jonathan01 said:
I am not sure about using 416 or not yet, i am leaning toward a SS, but may go with some type of regular steel.

I do not have a coolant drill. I have flood coolant, I think I am going to have to keep peck drilling it, and letting it cool.

I have a 135 split point drill that I plan to use. For the straighest hole, is it best to step up, say 1/8" to 1/4" than to the final 3/8"?

Thanks for all the help so far, I do plan on testing the hole in AL first.
Click to expand...
 
I have done this on 12L14 using a "D-bit". This is a shop made drill that has a single cutting edge and a short flute. I know there have been several threads about this, but I'm having trouble finding the one I was looking for. These bits cut slowly, but very straight. Never used them in stainless though, it tends to be tough and doesn't like light cuts.
 
It can be done. a few suggestions
1. do not try to drill all the way through with a small bit and then follow with a bigger bit.
2. Drill a pilot hole in a ways and then a larger hole always leaving a little bit of each size in the metal.
3. drill from both sides.
4. clear chip real regular, binding chips and metal welded on the end of the bit are a sure failure.
5. use brand new quality bits.
6. drill to a size under the desired size and then run the finished hole all the way through from one side to the other.
7.Put the bit in a chuck on an arbor in the head stock. while allowing the piece to be centered with a center drilled hole on a live center in the tail stock. advance the metal into the bit with the tail stock.
8. As long as possible keep the bar from spinning by holding it in your hand and allowing the bit to find its own way.
9. If you have to hold the metal tighter us a pair of channell lock pliers and still let the bit find its own way
10 Let the 2 inch bar rotate with the bit just a little, as the drill is cutting. By slowly letting the bar spin it will negate any tendancy for the bit to wander off center. With chanell lock pliers put a piece of leather between the pliers and let the work spin just a little bit. Like 2 RPM, just a little.
11. do not force the bit any harder than just what is needed to keep a steddy curl of metal coming. Pushing too hard will make it walk off center.
12. If you need a super precise hole finish the hole off with a D bit.
13 start with the faces of both ends faced flat and true.
14 Go for it with reasonable care the holes will hit dead on. I have done it many times making model cannons.
 
You must log in or register to reply here.
Back
Top