Boring bar speed?

[MRogersII]

Again, very new to milling....

Is there a "rule of thumb" conversion for boring bar speeds? I have found an abundance of tables on milling and drilling operations, and most of those have translated to acceptable finishes. But Ive found very little on boring bar usage. I assume that the answer is so simple, and so commonly understood elsewhere that maybe I'm the only one left who doesn't know.

My current applications are mild steel and aluminum, with internal ID's of 1.5 to 5".

Thank you

Michael

 

[Weldingrod1]

It's all surface feet per minute... just calculate your boring diameter. Just like turning the same od.

Sent from my SM-G892A using Tapatalk

 

[Bob Korves]

Again, very new to milling....

Is there a "rule of thumb" conversion for boring bar speeds? I have found an abundance of tables on milling and drilling operations, and most of those have translated to acceptable finishes. But Ive found very little on boring bar usage. I assume that the answer is so simple, and so commonly understood elsewhere that maybe I'm the only one left who doesn't know.

My current applications are mild steel and aluminum, with internal ID's of 1.5 to 5".

Thank you

Michael

Speeds and feeds - Wikipedia

en.wikipedia.org

milling feeds and speeds - Bing

Intelligent search from Bing makes it easier to quickly find what you’re looking for and rewards you.

www.bing.com

 

[MRogersII]

...it seems like every time I ask a question, the water gets deeper.

 

[Bob Korves]

It is really pretty simple. The larger the diameter, the higher the surface speed. Diameter times Pi (3.1416) times RPM gives you the surface speed. The surface speed is how fast your tool is moving over the surface. Machines work best when using an optimal surface speed, which is influenced by the rigidity of the machine, type of material you are cutting, and what material your cutting tool is made from. Some other more minor things, such as coolant and depth of cut, also affect how the tool cuts. None of this needs to be highly accurate. See how it cuts, and adjust the speed up or down until you get good results and a good material removal rate. The charts, and there are MANY out there, are just suggested starting points to start with...

 

[Mini Cooper S]

Nice thing about this forum, guys people can ask all the questions that you want, and those with a lot of experience will gladly share their wisdom.

Richard

 

[Manual Mac]

Sometimes if it is long bore, I will reduce the RPM & increase the feed to stop chattering.

 

[erikmannie]

I was just using Shars brazed carbide boring bars in a Shars 2” boring head yesterday. My mill is a PM-25MV (1 HP). I was boring from .500” to 1.900“ so there were dozens of passes.

The material I was drilling into was mild steel for 90 degrees and 6061 for the other 270 degrees.

I started at 330 RPM (at .500” diameter) and ended up at 209 RPM (at 1.900” diameter).

If the speed or feed is too fast, the mill will let you know (by stalling). If the speed or feed is too slow, you can tell because very little work is being done and it will be clear that you can get more aggressive (by increasing the feed and/or speed).

I would turn down the RPM as the diameter increased, of course, and I adjusted my feed so that the mill never stalled. If the feed is too slow, then the only penalty is that the job takes longer.

I am usually working on my own stuff in my home shop, so I figure I have the green light to get started with an RPM from the [Starting RPM = (Material Constant X 3.14) divided by Diameter)] formula and adjust the RPM up or down until I like how it is cutting.

The RPM value from that formula is just a starting point anyway, so I like to get cutting and see how it goes, making adjustments to feed speed along the way.

Also note that I am an inexperienced machinist, so I might be posting bad info here.

 

[7milesup]

A boring thread.
But lots of useful info here.

 

[MRogersII]

I am working on two boring projects. 1 - I am helping my Dad build two aluminum cylinder blocks (jugs) for an antique tractor. We started with two blocks of aluminum about 14" long, 10" wide and 6 1/2" thick. Each block has to be drilled (3/4") for the crankcase bolt holes and then two 5" cylinders bored into each one. The bolt holes are now drilled. I started the two cylinders with drilling two 1/2" holes, then 3/4" holes, then 1", thinking I would use a boring bar to be it out to 5". Very quickly I realized would need to live to be a very old man in order to get from 1" out to 5" with a boring bar. Now I am drilling a series of 1/2" holes around a 3 1/2" perimeter in order to remove the bulk of the center in one piece, with the intention of cleaning up and getting the rest of the diameter with my boring head.