I think I just learned something.

 I am trying to bore a 5 inch diameter hole in 6 inch diameter
 aluminum bar stock about 5 inches deep.

 I was getting tool chatter.  At first I thought I needed a stiffer
 boring bar. My boring bar is about .75 inch in diameter.

 I discovered if you speed up the carriage feed the chatter goes away
 more or less.

 Some of you guys on here are expert machinist.

 Have you heard of this before ?

 Paul Lamar

 Paul, The spindle speed formula RPM= Surface Feet per Minute x 4/
 tool Diameter SFM for aluminum is 400 & R is .002/.009 And the feed
 rate formula  Feed (rate per minute)= RPM x T (number of teeth) x R
 (chip load)

 Ray Hellstrom

 Thanks Ray,

 Interesting.

 Paul Lamar


 Paul, Are you using a carbide cutting tool? If so, a large nose
 radius can cause chatter. Also, I didn't mention that the depth of
 cut, which should be the adjusted with the speed to produce a
 continuous chip which forms due to plastic deformation of the
 crystal structure in the unmachined work surface and the shear occurs
 along the shear plane. As the cutting tool compresses the metal
 immediately ahead of the cutting tool, the deformation of the crystal
 structure elongates, the material above the cutting edge is forced
 along the chip tool interface and away from the tool.

 Ray Hellstrom


 No it is a sharp point.

 BTW do any of you guys know where I can get a six inch diameter
 steady rest?

 Paul Lamar

 Paul

 To the best of my knowledge, steady and follow rests are machine
 specific and not universal. I would start with the lathe
 manufacturer and get the model number.

 Bolton tools sells inexpensive Chinese made ones. It may be possible
 if your ways are reasonably close to the ones they offer- it might
 work for you.

 Alan Mullen Colorado

 My CC lathe is 40 years old. It came with a steady rest that is too
 small.

 I will make one out of a 10" by 10" steel plate .75 inches thick. A
 8 inch diameter hole will be cut in the plate with flame cutter. More
 on this shortly.

 Here is a picture of why I need it.


 Paul Lamar


 Paul, What about using a DoAll vertical bandsaw? From their website,
 most have a 13" vertical height, the bigger ones get more horizontal
 distance. Find a shop with one with the blade welder at the machine,
 With your height, DoAll might suggest the best blade and the pilot
 hole could be sized accordingly. Another thought. My old horizontal
 Kalamazoo bandsaw has a 19" horz. x 8" vertical space and takes a
 3/4" x .032 blade. Bore a center hole plus one just inside the ID,
 cut pie slices  Once you get the first pie slice out, the others
 don't need a rim hole.

 Jim Rudholm

 I have a Cheap Chinese copy of a DoAll. I am rather surprised that
 the quality of  Chinese products has greatly improved recently.
 Ironically that is part of the lack of U.S. jobs problem. China is a
 dictatorship and they are not playing fair when it comes to trade.
 They control the monetary exchange rate. Floating currency in most
 countries is an automatic means of balancing trade between countries.
 When the price on a given countries products goes up the demand goes
 down and that changes the monetary  exchange rate and tends to
 balance the trade. Not so in China. They fix the rate.

 We need a large tax or import tariff on Chinese goods to promote
 manufacturing here in the US. A small tax initially making it larger
 and larger until a balance in trade is reached.

 Now getting back to the machining problem. The band saw would work on
 both the six inch billet of aluminum and the new 3/4 inch thick
 steady rest. In both cases it would take a lot of time. The six inch
 billet is a one time operation and it is almost done. In the future I
 will use thick wall aluminum tubing for that part. I would still need
 the steady rest for my small lathe.

 The .75 inch thick steel plate for the steady rest would take a long
 time to cut an 8 inch diameter hole.

 I have a friend with a computer controlled flame cutter and he can do
 that in just a few minutes. No need to push the band saw slowly
 through thick steel. The saw needs to run at low feet per second rate
 to cut such thick steel other wise the blade gets dull. Also the
 radius is a bit tight for a band saw blade.

 Another option is water jet.  In this geographical  area that too is
 very expensive. On the airport we have a laser cutter and I will
 investigate that option next week.

 Thanks for making me think of my options :-)


 Paul Lamar

 Make your center support frame from 1/8" steel plate, welded up on
 the corners, hinged through the middle,  with bearings for support
 faces.

 Steve Carlisle


 You read my mind :-)

 That is what I had in mind more or less except it is 3/4 inch thick
 steel plate.


 Paul Lamar


 There will be four rollers about a half inch wide with small ball
 bearings. This will allow checking the run out and fixing it.

 The adjusting screws are 1/4 28. With fine thread screws like that it
 is possible to get the run out close to zero.

 Paul Lamar

 Here is what it will look like.

 Paul Lamar

Could this be done as a type of triangle where your rollers would come in about 20-30 degrees above the 180 degree plane?

Then your bottom roller would be at bottom center with the side rollers coming in at the 120 degree points?

Just asking. Not a mech engineer and it has been far too long since I worked in a machine shop (40+ years).

Regards,
Steve Thompson

Yes but that is harder set the run out to zero.

This takes the place of a live center when boring large diameter tubing.
A proper live
center will give you zero run out on both ends of the part.

I checked the price of a laser cut and the shop near me with a laser cutter could not handle
3/4 inch thick steel. They had water jet cutter but that was $300 and the cut surface was not perpendicular.

I wound up drilling about 50 or 60 .25 inch diameter holes around the circle. Then I cut it out with a 0.25 " wide band saw blade on the CC DoAll. Reminds me of how the Wright Brothers built their first crank shaft :-) Only they used a hack saw.

Then I plan on putting it on my rotary table and use a rough cut end mill to clean it up.

BTW I think I have some impure cold rolled steel. Some times the drill goes dull for no apparent reason. The steel and the drill where probably made over seas some place :-)

Paul Lamar

It is not unheard of to find hard impurities in steel especially if it is not
virgin steel or certified. Can you find a fabrication shop with oxy-acetylene
it should only cost a few dollars to do a small job like that?

Andrew Campbell


Yes I thought of that but I had a bit of spare time and did it this way mainly
for the learning experience.


Paul Lamar

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