Best Tool to Prep Before Fly-Cutting?

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SteveHGraham
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Best Tool to Prep Before Fly-Cutting?

Post by SteveHGraham » Mon Feb 13, 2012 6:36 pm

Today I made a 4.25" by something by something aluminum block to use as a spacer under a power transformer in a tube amp.

I had a piece of metal about the right size. I could have used it as it was, but I have a mill...

I used a fly-cutter to flatten one side. It took forever and required multiple passes because the band saw cut wasn't very flat. I decided to use a 1/2" end mill on the other side. It worked fine, but it was a little slow.

Should I be using something else to do this? I guess what I want is the right tool for roughing prior to fly-cutting.

It's amazing how the photo distorts the block.
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02 13 12 machined aluminum block for lamberson amp.jpg
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John Evans
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Re: Best Tool to Prep Before Fly-Cutting?

Post by John Evans » Mon Feb 13, 2012 6:57 pm

For light cuts try a face mill 1" to 2" inch or so.
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SteveHGraham
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Re: Best Tool to Prep Before Fly-Cutting?

Post by SteveHGraham » Mon Feb 13, 2012 8:24 pm

I need something that will do maybe .025" without a problem. Will a face mill that big work?
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davec43
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Re: Best Tool to Prep Before Fly-Cutting?

Post by davec43 » Mon Feb 13, 2012 9:10 pm

I was doing .050 with my 3" flycutter on some 7050 aluminum with no problem.
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John Evans
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Re: Best Tool to Prep Before Fly-Cutting?

Post by John Evans » Mon Feb 13, 2012 9:15 pm

Yeah,that is not not much DOC. BP style mills won't pull .250 DOC on a 2" face mill. I have 3/4 shank endmills to about 2" as I reacall a and a 3" indexable face mill for wide shallow cuts. Not a big fan of flycutters ,although I must have a 1/2 dozen of them in various sizes.
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Michael_Moore
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Re: Best Tool to Prep Before Fly-Cutting?

Post by Michael_Moore » Mon Feb 13, 2012 9:32 pm

2" face mill and lots of shielding because it will throw chips all over the area around it!

A large diameter flycutter can give a very nice surface, but it is slow. My 2" insert mill has 5 inserts so you can up the feed significantly from a single-point fly cutter. GWizard shows that a single flute 2" OD indexible cutter with .062" DOC and 2" cut width in 6061 aluminum would be 1843 RPM and feed at 12.9 IPM. Change that to a 5 insert and you get the feed bumped up to 64.5 IPM. A single point 10" OD cutter with the same DOC and a 2" width cut goes to 550 RPM and 4.8 IPM feed

One thing to keep in mind with a fly cutter (or other large diameter cutter) is that the quality of your head tram will show up in how flat you can get the part. Consider that if you were to face a 9" wide plate with a .010" EM with a .007" step over the head could be pretty out of square and you would still get a pretty flat surface (but it will take some time). Switch to a 10" diameter cutter and a very slight amount of tilt is going to leave the center of the cut a lot lower than the edges.

So if you've got a mill that you just can't tram in (think of a rigid ram that has been crashed really hard so the ram/column are bent) you may get better results with a smaller diameter cutter.

cheers,
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Re: Best Tool to Prep Before Fly-Cutting?

Post by Harold_V » Tue Feb 14, 2012 1:57 am

SteveHGraham wrote:I need something that will do maybe .025" without a problem. Will a face mill that big work?
It is my opinion that you should avoid face mills larger than about 3" for a BP type machine. They don't have the necessary horsepower nor the rigidity to warrant such a large cutter, but why you can't take a decent cut with a fly cutter escapes me. With a single tooth, they tolerate a much deeper cut than you could pull with a face mill. How deep were the passes you took? I can't imagine that you couldn't take at least .05" per pass, and likely more. What's going on, Steve?

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SteveHGraham
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Re: Best Tool to Prep Before Fly-Cutting?

Post by SteveHGraham » Tue Feb 14, 2012 10:07 am

Harold_V wrote:How deep were the passes you took? I can't imagine that you couldn't take at least .05" per pass, and likely more. What's going on, Steve?Harold
A long time back, I had an incident where my fly cutter started dropping into the work as the table moved. I tried to find out why this happened, and the best answer I got was that if you put too much horizontal force on a fly cutter in a collet, it can descend while it's running.

Yesterday I was trying to fix this wavy surface, and I saw that it was hard to predict how deep the cut would go, because the humps in the surface were hard to spot. That meant I could either take a deep cut--maybe .030"--and risk having the cutter drop, or I could take four or five shallow passes, which would take a very long time.
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Patio
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Re: Best Tool to Prep Before Fly-Cutting?

Post by Patio » Tue Feb 14, 2012 10:40 am

Steve I have a Shaper that if the tools geometry is not proper will dive into the work.
A tool shape, with rake and too much relief will create great forces, pulling the tool into the work.
The forces can be controlled by decreasing the relief, adding lead or decreasing the amount of rake.
Theoretically if all these angles were set right, the tool would ride through the material, with the only force being in the direction of the cut.

This is the way I understand tool geometry to work, with my limited amount of knowledge of 14 months. :)

This was recently discussed here on the board. Harold may remember the thread, I would need to do a search to find it.

More knowledgeable people than me will chime in I am sure.

Edited to add search results:
The search function is your friend.
You were a contributor to this thread that discussed this topic, where Harold wrote a considerable post on the subject of tools pulling into work.
http://www.chaski.org/homemachinist/vie ... ad#p231817
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stevec
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Re: Best Tool to Prep Before Fly-Cutting?

Post by stevec » Tue Feb 14, 2012 12:01 pm

Pat, is the toolholder you are using in your shaper the proper style or is it a "lathe" style toolholder, such as the ones often seen in a lantern style toolpost? They are a no-no for a shaper for the reasons you have pointed out.

f350ca
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Re: Best Tool to Prep Before Fly-Cutting?

Post by f350ca » Tue Feb 14, 2012 12:33 pm

I have to agree with Steve on this one. I use the angled lathe style ones to cut dovetails as I can run a shorter cutter and still reach into the angle, But they do like to allow the tool to slip.

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Re: Best Tool to Prep Before Fly-Cutting?

Post by stevec » Tue Feb 14, 2012 3:34 pm

Greg, I wasn't talking left or right angled toolholder I was thinking of the upward angle the tool is held in a Lathe toolholder as opposed to the straight held tool of a shaper toolholder. Looks a bit like the old lantern style tool post holders for brazed carbide bits.

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