How to bore this hole?

[kvom]

On my CO2 engine build, I need to bore out the crankcase, flat bottom hole 1.5" in diameter and ~1.75" deep. I have a 3/4" diameter boring bar and a boring head with a ..75" shank. The boring bar necks down to .625" at the cutting edge, and I have a 41/64" drill bit (.64") to drill the pilot hole before boring.

I can do this on the mill, but there is an issue of chips accumulating in the bottom of the hole. So using the lathe would be better. My problem is that my AXA holders won't take the boring bar. So my lathe option is to chuck the boring head in the tailstock and use the tailstock to feed the cutter.

Is there any downside to doing it this way? Neither of the hole's dimensions are critical, although it shouldn't exceed depth by more than .05".

I can also take the block to school and turn it there as the lathes have CXA boring bar holders.

 

[steamer]

KVOM,

I would make up a boring bar to suite. You will have a lot more control and a more ridgid set up with a bar in the tool holder than a boring head in the tailstock.

You could use a broken center drill as a tool and bore a hole in a piece of stock to suite.

In the end, you'll have another piece of useful tooling for the lathe.

Dave

 

[Mainer]

Is there any danger of the boring head loosening in the tailstock? If it's held by a taper socket, which I assume it would be, I would be leery of trying it. Other than that, I don't see any particular problem.

Personally, I would probably try to either get a holder to hold that 3/4" boring bar, or get a boring bar that I could hold in my toolholder.

Another option would be to do it on the mill and have a vacuum cleaner running to keep the hole clear.

 

[putputman]

It looks like the ideal time to stop and make a 3/4" boring bar holder for that AXA. I have one that holds a 3/4" bar that I use very often in engine builds. They are very sturdy.

 

[jpaul]

K, you don't say what material your engine case is made of but if the case is mild steel or aluminium, I would consider using a smaller boring tool. Certainly a 1/2" boring tool would be stiff enough for your project. If the engine case is aluminium I would think that a 3/8" diameter tool would be sufficient.

This may be a good time to expand your inventory of boring tools. Take a few minutes an fabricate the tool you need. You can't have too many boring tools.

 

[Cedge]

Kvom
When I needed to use a larger boring bar I had on hand, it was about twice the size it needed to be to fit it in the tool holder. I milled a block of 1.250 inch of square aluminum to fit the tool holder and then used the lathe chuck to drill a .75 in hole for the boring bar. Add a couple of screws to secure the boring bar and mount it in the tool holder. Worked like a champ.

Steve

 

[joeby]

Do you have any long endmills with a 1/2" or 5/8" shank that are long enough? You can hold the shank in your tool post and align one cutting edge to center, be careful you don't hit the bottom of the hole too hard though.

Boring bars don't take much time to make, especially if you just drill a 1/4" hole in it and use broken centerdrills or endmills for bits.

Kevin

 

[kvom]

Thanks for all the good options.

Crankcase is aluminum.

I do have a piece of 1.5" square aluminum bar that would be excellent for Steve's method, so it's likely I'll try that in any case. I'll also try to grind one from a 1/2" HSS blank.

 

[kvom]

I asked my shop instructor the same question, repeating the various suggestions posted here, and he confirmed just about everything I read. You guys rock! ;D

So I took a piece of 1.5" square aluminum and drilled a 3/4" hole through it. Today I will make a holder like Cedge's. I also got a broken 2-flute end mill and ground it to use as well. And finally I have a 3/8" HSS bit that I found in the misc. tools I got with the mill that will work for small holes. Looks as if I will be boring soon.

I have a cylinder mounted in the 4-jaw from yesterday that will become the trial piece. It will be bored through, so easier than a flat-bottom.