Boring heads for beginners

[jwmelvin]

I needed a 3.5” hole through a 0.75” thick 6061 plate and used a hole saw (with four circumferential 0.25” holes for chip relief). I don’t care so much about precision because I will be welding a 3.5” OD pipe in. But it would have been nice to size it as desired.

I don’t have a rotary table, which would have let me use a mill to finish the note, as I understand it. Is another option a boring head? Does a 3” boring head make holes no larger than 3”? I also realized that I needed some 1” holes so I had to order large drill bits but it seems I could use a boring head for that?

I have a PM-30MV mill.

 

[Ed ke6bnl]

the boring heads are adjustable and you creep up on the desired hole size.

https://www.ebay.com/itm/HFS-12Pc-3...925546&hash=item3f81c6827f:g:u2oAAOSwIeFbPb-E

 

[Chipper5783]

A boring head will go about 2x the size of the head. It will also go quite small (i.e a 1/4" hole may be a challenge - but doable). Also, for medium size holes (about 1.25" dia) the annular cutters are a good option.

 

[jwmelvin]

I got the creep-up-on-it aspect but thanks for the info on hole-size range. If I needed multiple holes of a certain size then an annular cutter seems good.

Is a 3” head too big for my mill in practice?

 

[rwm]

That's an awful nice hole. What kind of hole saw did you use?
Robert

 

[jwmelvin]

That's an awful nice hole. What kind of hole saw did you use?
Robert

Thanks. It chattered a bit in the beginning but settled in okay. It was a new Milwaukee bit at around 85-100 rpm with plenty of tap-magic.

 

[rwm]

A standard one lined with steel teeth? I have seen new ones with 4 evenly spaced carbide teeth. I have been wondering how they work.
Robert

 

[jwmelvin]

A standard one lined with steel teeth? I have seen new ones with 4 evenly spaced carbide teeth. I have been wondering how they work.

Yes a standard bit: https://www.homedepot.com/p/202327759

I saw some carbide-tipped bits of another brand but they didn’t have one in 3.5” so I couldn’t try one.

 

[Chipper5783]

I got the creep-up-on-it aspect but thanks for the info on hole-size range. If I needed multiple holes of a certain size then an annular cutter seems good.

Is a 3” head too big for my mill in practice?

I am not familiar with that machine (had a quick look on the PM web site). You need to respect the surface speed for the selected tooling - so if you want a large hole then you need a slow speed. The specs claim the low speed is 50 rpm, but does it have any torque down there? Also, you are only working with an R8 taper - which is fine, but don't try to push it out to too large a diameter. You should be fine with a 3" hole in aluminum. At worst you may be forced to take very light cuts and play around with the tool grind. Another consideration is how much head room you have (Z-axis). That is a small mill and the Z room gets eaten up in a hurry. When looking at boring heads, don't get one that is larger than you need, since bigger ones are also taller (check the specifications).

 

[mikey]

Is a 3” head too big for my mill in practice?

A 3" boring head is way too big for your mill. A Criterion DBL-202B, a 2" head, will bore a hole from 0.050" ID out to over 6.5" ID and would work very well on your machine. The real issue with a boring head insofar as how large you can bore (up to the limit of the head) is your available speeds. The larger the hole, the slower you must be able to run in order to keep centripetal forces under control.

A 2" boring head would have made short work of that hole you needed, and the sides would be vertical and the finish would be finer. How accurate it would be depends on how good you are with a boring head.