A Question On Machining

[prasad]

May I suggest that you go on ebay and find a small boring bar? Micro 100 sells some really nice ones that will do this job easily.

The reason I suggest boring is because a reamer will follow a crooked hole. It will have a nice finish but the hole may not be straight. A boring bar will cut the hole straight AND give you a good finish; how accurate the bore will be depends on your skills when you bore it.

Hi Mikey

I received the Micro 100 boring bar. It is really tiny. However I am not sure how to hold it in my tool post. Is there a dedicated holder to hold it? I searched the Internet and unable to find one. The boring bar I received is "BB 100600" i.e., 0.1 inch minimum hole and 0.6 inch max depth.

Thanks for your advice
Prasad
Eastern PA

 

[Wreck™Wreck]

You make a tool holder, drill then ream a bore through a square or round steel bar, drill and tap some set screw holes then place into the tool post.

 

[rlgustin]

Yes a lot of times we of times we make or own special tool holding devices. This is the fun part of what we do.

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[mksj]

You can also mount the boring bar in a square/rectangular shank with some set screws to lock it in place, then put that in a standard insert holder. I would use a dial/indicator gauge to make sure the platter is running true in both axis when you chuck it up.

 

[tq60]

Start over and change order of operations.

Repeat as before and make front side.

But do not finish cut but get close.

But first use a mallet and tap against the stock as you tighten the jaws and rotate the Chuck and repeat this.

You will hear a different tone when the stock is flat to chuck.

When drilling hole use short drill and

Now get a bolt that is a very snug fit in your hole and find one the is not threaded where it interfaces with the work

Better would be to thread some stock so it can be placed in the Chuck then simply remove nut to remove disk, this is a mandrel approach.

Tapping against chuck should have made it flat.

Now place on mandrel and take tiny finish cuts to final size.

Flip to clean up back side.

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[Christian Poulsen]

Yes as said above by some, and assuming you indicated dead on (.25?!!, even .025?!!)...anyway assuming you indicted dead on when you flipped the part and the motor shaft is not bent or running out of concentricity or something is going on with that...
...even a tailstock that is trammed in (adjusted) (push/pull for y) and shimmed for Z ) and the part is center drilled nice or the centerdrill hole angle is "kissed" with a toolbit; Will not drill dead on...so boring to size after undersize drilling is the way....
....You can save this part as aluminum is easy to plug...bore your part, lets say 1/2" oversize (with a nice finish)...turn a plug with a nice finish (I like about .001 oversize just eyeballing your boss OD size and hole in the picture but .001 per inch press (dia) is a rule of thumb for soft steels and alum.) ...turn the plug length oversize too (say 1/4" "longer" for some meat to press or pound on)....put a little lead in on one end of the plug and press (or pound the heck out of it) in...be sure to get it started straight on a flat supported set up and use shims or something to make sure the plug goes at least a couple of thousands through past the lead in and once it starts going don't stop until it goes through (antiseize (lube) is also nice to use)
...then indicate the faces of your part and face the prodruding plug ends off nice and indicate all again and center drill and drill undersize and bore to size (don't get it it too hot while remachining as if the part gets too hot it may grow and the plug will loosen')

PS The Turkey is on the smoker and will be done at 1:00...Happy Thanksgiving everybody!

 

[Christian Poulsen]

Start over and change order of operations.

Repeat as before and make front side.

But do not finish cut but get close.

But first use a mallet and tap against the stock as you tighten the jaws and rotate the Chuck and repeat this.

You will hear a different tone when the stock is flat to chuck.

When drilling hole use short drill and

Now get a bolt that is a very snug fit in your hole and find one the is not threaded where it interfaces with the work

Better would be to thread some stock so it can be placed in the Chuck then simply remove nut to remove disk, this is a mandrel approach.

Tapping against chuck should have made it flat.

Now place on mandrel and take tiny finish cuts to final size.

Flip to clean up back side.

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....with all due respect TQ, tapping the finished side against the jaws of a chuck (even a good unworn one) is assuming too much for the opposite side to be machined parallel to it and therefor the hole to be straight too...to do it right, besides indicating any ods/id to each others sides, a test indicator should be "hooked" over to that finished face (chuck side) and tapped in (or "out") to dead on...if'n that back side (face) is out even, just say .002, at around the 6" dia. the hole will be out of "straight" (yada, yada)
...but yes, a mandrel/arbor set up with a decent OD size and "kissed" flat and parallel face is nice too....

 

[mikey]

Hi Mikey

I received the Micro 100 boring bar. It is really tiny. However I am not sure how to hold it in my tool post. Is there a dedicated holder to hold it? I searched the Internet and unable to find one. The boring bar I received is "BB 100600" i.e., 0.1 inch minimum hole and 0.6 inch max depth.

Thanks for your advice
Prasad
Eastern PA

As Wreck and the others have said, I would make a tool holder out of square stock. Just plain mild steel keystock from the hardware store will do. There are two ways to do this simple job that I can think of - one would be to put it in your 4JC and drill and ream a 1/8" hole and tap two holes for screws to hold the boring bar and lock that in a standard tool holder; the other would be to use a slitting saw and cut a slot from the side of the square stock into the slot. When you tighten your tool holder screws down onto the boring bar holder it will compress the slot and hold the bar solidly. I would favor the latter approach; I dislike clamping down on small diameter carbide tools - while unlikely, they do crack.

Whichever way you go, I would orient the flat at the tip of the bar so it is horizontal. You can turn it a degree or two to achieve some positive rake if you choose as long as you have enough clearance under the cutting edge. That carbide bar, small as it is, will hold pretty tight tolerances so go slow, measure often and you'll be fine.

Let us know how it goes, Prasad, and a Happy Thanksgiving to all!

EDIT: Sorry Prasad, I forgot to ask if you have a boring bar holder. In that case, make a simple sleeve on the lathe, drill and ream it and slit it down the side. Then stick it in the holder and you're all set.

 

[rlgustin]

Some of the best challenges I have ever had was saving a part that was wrong. Take your time make sure your setup is sound and good luck. You've received some very good advice. Happy Thanksgiving.

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[tq60]

....with all due respect TQ, tapping the finished side against the jaws of a chuck (even a good unworn one) is assuming too much for the opposite side to be machined parallel to it and therefor the hole to be straight too...to do it right, besides indicating any ods/id to each others sides, a test indicator should be "hooked" over to that finished face (chuck side) and tapped in (or "out") to dead on...if'n that back side (face) is out even, just say .002, at around the 6" dia. the hole will be out of "straight" (yada, yada)
...but yes, a mandrel/arbor set up with a decent OD size and "kissed" flat and parallel face is nice too....

You tap it against the Chuck on the rough cut.

If you wish to dial it in fine but that is for after you have it on the mandrel.

If the face of the Chuck is such that seating the work against it causes it to be off due to uneven face then the Chuck is not suitable for work.

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