"Reverse Boring" (Horizontal Mill) Sanity Check Requested

[G-ManBart]

Okay, I'm not really sure what to call it, but I'm going with "reverse boring"! I want to bore out an NMTB 50 end mill holder from 7/8" to 1.25" so I can adapt it to an arbor I have that won't fit the K&T. I'd like to bore it while mounted to the mill so the hole is perfectly aligned with the spindle. My first thought was to grab a boring bar in a QCTP holder and secure that in the vise, as pictured. My concern is that downward pressure on the insert tip might cause the holder to move in the vise (the back would rise). The boring bar projects from the side of the holder enough to make solid contact along the length of the vise jaw. That should somewhat support the front and help resist movement, but no telling how much. I could change and put parallels under the QCTP holder so that the boring bar isn't making contact at all, but I'm not sure that offers any benefit since the holder could still rise up off the back of the parallels...probably a bit more support up front though.

Maybe I should just clamp the boring bar directly to the table with hold downs? I'm thinking of trying the pictured setup with light cuts, see if the boring bar/holder moves at all and if it does switch to another method like clamping it to the table.

Is there an easier/better way I'm overlooking?

For those interested, I'm making the Franken Arbor for my K&T 2H for a couple of reasons. I didn't have a 1" diameter arbor of any kind, but have a pretty good pile of 1" cutters for starters. Then I stumbled onto a really nice German made NOS 1" arbor at a local machine supply place, but it has the wrong mount (reminds me of a long Jacob's taper or similar). It's a nice length and came with a full set of spacers and two running bushings, for $50....had to buy it. I'm going to shorten and turn down the mounting end so it's 1.25" diameter and a bout 2" long so it will fit the NMTB 50 end mill holder.

Shar's finest The vise has slots on either side of the screw and I may see if there's a way I can run a bolt up from that and put a plate across the top of the boring bar and vise jaws like a makeshift hold down. Nothing is tightened down in this picture as it was just a concept to line things up...I'll tighten all four set screws when ready.

 

[francist]

What would you think about a pair of v-blocks in the vise with the boring bar held between those? If the blocks are resting on the floor of the vise there should be little opportunity for them the shift around. That way you get out of using a separate tool holder block altogether. Depth of cut on the bar would be gained by advancing your left-right feed ("X") on the mill table.

 

[Chipper5783]

Should be fine. It doesn't really matter how you hang onto the boring bar (minimize overhang - no different than a lathe). Strictly speaking you won't have the correct set screws in your "new" 1.25" holder (no doubt there will be a standard for the design of a end mill adapter).

 

[T Bredehoft]

Just a suggestion, tighten all four screws. And a wild idea. Put a piece of kraft paper (brown butcher's paper) on both sides of the holder and tighten the bejesus out of it.

 

[G-ManBart]

What would you think about a pair of v-blocks in the vise with the boring bar held between those? If the blocks are resting on the floor of the vise there should be little opportunity for them the shift around. That way you get out of using a separate tool holder block altogether. Depth of cut on the bar would be gained by advancing your left-right feed ("X") on the mill table.

I thought about that, but don't have v-blocks small enough (they are on the list). I have a long makeshift v-block I use for holding round stock in my bandsaw that might work...didn't think of that until your suggestion. Thanks!

 

[G-ManBart]

Should be fine. It doesn't really matter how you hang onto the boring bar (minimize overhang - no different than a lathe). Strictly speaking you won't have the correct set screws in your "new" 1.25" holder (no doubt there will be a standard for the design of a end mill adapter).

You're right about the set screws. I looked at a number of 1.25" end mill holders and some have one set screw and some have two. I'll only have one, but it's fairly large diameter and I'm planning to make the arbor tight in the holder so the set screw should mostly be to prevent rotation. Honestly, if I really like how it turns out I could easily TIG weld a couple of tacks to secure the arbor to the holder....shouldn't put enough heat in it to warp anything.

 

[G-ManBart]

Just a suggestion, tighten all four screws. And a wild idea. Put a piece of kraft paper (brown butcher's paper) on both sides of the holder and tighten the bejesus out of it.

I should have mentioned I was just setting things in place for the picture and nothing was tight so the boring bar wasn't in final position, etc. I'll definitely tighten all four screws and the kraft paper is a great idea...thanks!

 

[benmychree]

Have you determined that the end mill adaptor is machinable? Generally, they apr pretty hard.

 

[rabler]

Your toolholder is somewhat off center in the vise. Typically that will put more pressure toward the center of the vice. I'd put parallels under the tool holder, and/or put something the same thickness (such as another toolholder) on the other side of the vice.

 

[G-ManBart]

Have you determined that the end mill adaptor is machinable? Generally, they apr pretty hard.

I'm not certain, but looking down the bore it appears to show evidence of turning past where the end mill would be (I assume they grind that area for exact dimension). I figure I'll find out quickly if it can't be machined.