Enlarging bushing capacity

[Julio Navarro]

I have a mortiser that has a 3/4" I.D. chisel bushing. I have a bunch of 5/8" dia chisels from Jet that I cant use on this mortiser. I bought a 3/4" O.D. x 1/2"I.D. bushing (I could not find any 5/8" I.D. bushings) This bushing fits nice and snugg in the stock 3/4" I.D. bushing that came with the mortiser.

I figure I could bore the 1/2" I.D. to 5/8" but I dont know what sort of drill/burr/other tool to use to enlarge the bushing.

Would a deming drill bit work, or any carbide bit work?

I have a DP that would do the job just need to know what sort of bit to use.

Thanks as always.

[Steve Clardy]

H.S.S. bit should work ok.

[Julio Navarro]

H.S.S?:o high strength steel?

[Steve Clardy]

High speed steel.
Use low speed, with a coolant. Oil, thread cutting oil, etc.

[Cliff Rohrabacher]

High speed steel.
Use low speed, with a coolant. Oil, thread cutting oil, etc.

That is "slow" as in you can count the spindle revolutions out loud as the drill turns. Keep an eye on the heat build up in the chisel. To much heat and you'll have softened (over tempered) the steel in the chisel. Don't let the chisel get hotter than 350-F absolute maximum. Even a couple degrees beyond 350-F and you'll screw up the chisel.

If those chisels can be sharpened with a file then you can work the metal with HSS. Carbide is better but carbide requires a level of stability you won't get in a wood working drill press.
Carbide would let you run faster but the chisel might not tolerate the heat.

Wear your eye protection!

[Julio Navarro]

Thanks guys, will report back

[Steve Clardy]

That is "slow" as in you can count the spindle revolutions out loud as the drill turns. Keep an eye on the heat build up in the chisel. To much heat and you'll have softened (over tempered) the steel in the chisel. Don't let the chisel get hotter than 350-F absolute maximum. Even a couple degrees beyond 350-F and you'll screw up the chisel.

If those chisels can be sharpened with a file then you can work the metal with HSS. Carbide is better but carbide requires a level of stability you won't get in a wood working drill press.
Carbide would let you run faster but the chisel might not tolerate the heat.

Wear your eye protection!

He's boring a bushing Cliff, not a chisel;)

[Brian Hale]

Good advice has already been given but my question is how are you going to hold the bushing? A 5/8" bit spinning at ~250 rpm creates an amazing amount of torque and (i assume) since the bushing is round you'll need to grip it securly without crushing it.

I'd suggest doing it in a lathe if possible.

Brian :)

[Julio Navarro]

Brian:

I am going to try the BP using a vise and using the lowest speed,oil, and lots of face protection.


If that doesnt work or if it feels the least bit iffy, I will probably try and find a metal shop somewhere and have them do it.

I have looked everywhere for a 1" O.D. x 5/8" I.D. and I cant find one.

But to answer your question, yes, I do anticipate that it will be hard if even possible on the BP.

[Brian Hale]

The BP will have plenty of power, no doubt about that.

I'd hold it in the vise using a pair of "V" blocks if possible and sweep the ID with a dial indicator to make sure you're centered.

If it doesn't work out for you, let me know and i can hook you up with one of our programmers that does manual machining on the side and he can either make you a new one or drill out the one you have.

Brian :)

[Bruce Wrenn]

My first choice would be to do this operation on a metal cutting lathe. It is a simple machineing operation. Check with local tech college and see if machine shop class could do it as a "Live" project.

[Julio Navarro]

Well, I tried to enlarge the ID by drilling with a 5/8" HSS bit and it worked fine. It wasnt very difficult, only problem is it was off center rendering the bushing pretty much useless.

Fortunately, the bushing was only about 5 bucks so I will probably get another one and try again. I may get a short deming bit. It looks as though the shorter the better chance to get it on center it is.

Bruce, I think the trade school is a great idea except there are no trade schools around here! I looked when I wanted to learn welding. I still find it hard to belive that. But it is a good idea.