Criterion 1-1/2" Boring Head

[dlane]

Bored a hole in 1" aluminum on my supermax 9 X 42 bport clone , opened the boring head all the way open
To bore a 1. 554 hole . Don't think the mill liked that much it was kinda shaking , now the nod is off .
Vfd set to 17 hrtz , belt on fastest pulleys, guess I need a tach .
Question : do these things need to go reeealy slow ? Any hints , that was my first boring experience
Guess I need to watch utube a little more
Thanks

 

[extropic]

The type of boring heads you mention are chronically "out of balance" and should be run at very low RPM. Try 50-150 RPM and see how it goes.

 

[Firestopper]

^^^This^^^ I recently bored out the lathes belt/end cover from 2.250 to 2.750 using this method. I try to choose a bar length that gets the job done without too much "off center" adjustment. Those inexpensive carbide tipped boring bar sets work well on most aluminum leaving a nice finish.

This bore was done in .033" increments at 400 rpm and manually feed using inexpensive bar with no lube.
The cutting end must be set up (rotated) to contact material correctly, I eyeball this for the most part. You'll know if you have it set up correctly on your first light pass by feel,sound and finish quality.
Adding a tach would help a bunch.

 

[Wreck™Wreck]

Put a piece of round stock in the unused hole opposite the tool and adjust the length until it is roughly balanced and bore away.

 

[Profkanz]

My students use this method to bore holes out up to 2.0" in aluminum every semester. I do not let them run over 350 RPM. At that speed we have no problem.

 

[dlane]

If there is a next time with this head I will run it really slooooow ,

Wreck this head only has one tool hole in bottom center.

Need to re tram the head and re level mill now.

 

[Chipper5783]

dlane, you wrote that you ran the head on the fastest pulley and 17Hz (very slow) on the motor. Interesting combination, why not run on the slowest pulley and pick the motor speed up a bit? Suggest starting with a surface speed of 50 ft/min - for your hole size of just over 1-1/2" about 130 rpm - then adjust from there up/down until it cuts nicely. With aluminum, it ought to let you go quite a bit faster - depending on lots of other things.

I can see where a tach would be sort of cool, but it would be straight forward to make up a chart of Hz to spindle rpm for the various pulley combinations. It doesn't take long to gain the experience to figure out when the speed "seems about right". I admit to not having speed indication on any machines and don't think this hinders me (perhaps I don't know what I'm missing?).

 

[dlane]

Thanks David, I may try to make a speed chart , I first started at 35hz that's when the shaking was worst . Probably should of changed the belt setup though

 

[sanddan]

I just did a similar job as firestopper using a 3" shars boring head running at about 150-200 RPM. I was getting a crappy finish until I switched the down feed to the middle position (slower), that gave me a decent finish. No idea if the cutting edge was aligned correctly, I just eyeballed it to be 90 deg to the edge of the hole. I did notice that the boring head had a ton of run out between the head and the R8 shank. Hated looking at it during the boring, just makes me want to upgrade to something better. It did work just fine though.

I second the wish for the tachometer. I'd love to have one on the mill.