First time to use a boring head in the mill HELP!

[Mr Fixit]

Hi Group,

Newbie question here.

I have a BP clone and want to do a hole, offset to one side (making a eccentric BB for a tandem bike) in a 3" round piece of aluminum .50 thick. The hole will be drilled close to size and then I will attempt to use the boring head to finish cut the hole to a press fit size of 1.65" for a steel sleeve. The head that came with the mill is a Criterion .625 straight shank head. I have a R8 collet to fit and have a carbide tool from one of the regular boring bar sets in the wood blocks from who I'm not sure. I have checked the sharpness with the 10x loop and feel I'm OK on this part.

So my question is, how do I set this up for boring the hole drilled in the mill, keeping the same setup, after changing the tooling to bore. I see the allen wrench adjuster for 1div=.02MM where do I set the tool bit in relationship to the hole. Is It like boring on the lathe, touch off on the hole and adjust the table for depth of cut?

Do remember I'm a HSM newbie, and am self trained with your help from my questions posted here from time to time and lots of reading here and other places..

I look forward to your answers.

TX
Mr fixit for the family
Chris

[lakeside53]

Orient the tool bit such that it it slightly positive in rake but no rubbing on the underside. Make a very light cut with your power feed and measure the hole - that is now your reference. Surface finish has a lot to got with accurate measurement so take care. Be sure to account for backlash if you go over an adjustment and back up (back up then go forward again). Measure often... that dial isn't all that accurate if you are striving for sub 1 thou fits.

[Erich]

Lock both tables then drill the pilot hole.
Swap in the boring bar. Use the allen screw on the boring bar to increase the radius the cutter swings.
As you get close take multiple "spring cuts" then measure bore with telescoping gages or a real bore gage.
Calipers won't cut it bore a press fit.

[lakeside53]

Unless you need to remove the sleeve, use heat on the aluminum. Bore 1-2 thou undersized, heat 275-300F and drop the sleeve in.

[SGW]

Speaking from personal experience...you may want to get an R8 shank for your boring head. I had what you have -- a 5/8" straight shank, held in a collet -- and I found that it was not sufficiently rigid. The length of the boring head plus the length of the boring bar makes a long lever arm. With that setup, take light cuts, and as Erich suggests, spring cuts, to minimize flexing. You'll be boring aluminum, so it won't be as difficult as boring steel.

I find that it's useful to lock the boring head by tightening the dovetail adjustment screws before taking a cut.

Don't have the RPM too high. If a 1/2" diameter end mill should turn at, say, 750 rpm when cutting a given material, a boring head set for 1.65" diameter should turn 750 * (.5/1.65) = 227 rpm.

[john hobdeclipe]

Make sure that there is room under the hole for your bit to come through without hitting anything.

Use your machine's self feed capability. You'll get a much smoother finish than feeding by hand. Set the feed to kick out just after the tool has cleared the bottom of the hole.

Depending on what you have available for measuring the hole diameter, you may consider making a "go-no go" gage before you start boring the hole.

[Mr Fixit]

WOW Guys,

This information is GREAT, and exactly what I need to keep moving forward on this project. My daughter is building a tandem bike for her and my grandson. We've got the frame complete with the exception of this machine work. We both really appreciate your help in sharing your Knowledge, and we look forward to riding this bike in the next couple of weeks.
I will post a pic or 2 (not on PB) of the final project.

TX
Mr fixit for the family
Chris

[R.Bolte.Jr]

THIS!!!

...Depending on what you have available for measuring the hole diameter, you may consider making a "go-no go" gage before you start boring the hole.

It seems like I never have enough room under the boring bar to ACCURATELY use telescoping gauges or internal mics. Take the time to turn up a shorty gauge of a few thou steps if fit is critical.

[Norman Bain]

Do work out early if the "gauge" on the boring head measures in "change of diameter" (like most lathe cross slides do) or "change in radius" (which means you need to move it half the amount you think you need).

[Mr Fixit]

Hi Gang,

Norman I did just that on a scrap piece to figure out the tool and the adjustments. I have don't the final job and it came out perfect in my opinion. I was spot on for size and took Lakeside53's suggestion of heating the aluminium and the parts just fell together. Now the daughter is finishing the frame at home for painting and final assembly. When it's rolling I will post a pic of the final product.
It was real fun working with her and a girl friend who is her biking pardner, we even got the 10yr old grandson to design the head badge to be made out of brass sheet stock to be cut out and formed. He's excited to be a contributor and making a part of the project.