Another fly cutting question.

[John TV]

Second fly cutting question from the nuub.

First time fly cutting, had issues with hard spots and used braised carbide lathe cutter to address the hardness but the bit had no radius in the cutting tip. So finish was not great.

My question is about how the cut changed on my mill based on the table feed direction. Should direction of table travel change the cut quality?

This first two pics show travel left to right with clockwise cutter rotation.

The second pics show left to right table with clockwise cutter rotation.

There is a significant difference in cut quality and it seems left to right is much cleaner.

Is this my old mill wear and tear showing up or tram issues or ? Your thoughts are appreciated.

John in MN


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[mmcmdl]

You should see your cutter marks going this way ((((( as well as this way ))))) when perfectly trammed . Kind of similar to a Blanchard grinder finish .

 

[mikey]

My question is about how the cut changed on my mill based on the table feed direction. Should direction of table travel change the cut quality?

This first two pics show travel left to right with clockwise cutter rotation.

The second pics show left to right table with clockwise cutter rotation.

John, I am confused by the bolded sentences above - they seem to say the same thing or am I missing something.

Regardless, try to look at a fly cutter like an end mill with a big swath. Unless your mill is big and really rigid, it is better to conventional cut when doing stock reduction and climb cut when doing fine finishing cuts. Adjust the stick out of your tool from the flycutter body to the minimum required to span the part. With the body of the flycutter behind the part, adjust the table in Y so that the tip of the tool reaches past the edge of the part closest to you. Now move the part to the left in X so the flycutter is clear of the part and set your depth of cut in Z. Now feed the table to the right to engage the flycutter; this is a conventional direction of feed. Make a complete pass so the flycutter clears the part and see what you have. If you like, dial in a few thou more in Z and feed the table back the other way, from right to left, and this will be a climb cut that should produce a better finish.

You need to have enough speed (remember the formula: RPM = SFM X 3.82 / D, where D is the diameter of the swath of your flycutter) and you need to feed fast enough to keep the tool cutting continuously. Give this a try and get back to us.

Oh, if you're still using that brazed carbide LH tool, put a tiny nose radius on it with a diamond stone and use cutting fluid.

 

[John TV]

Mikey,

You are correct, typing error on my description, the second set of picks was RIGHT TO LEFT. Thanks for catching that.

I will give your suggestions a try. Thank you.

I'm still confused by the concept of climb vs conventional milling when the cutter is larger than the piece so it clears both edges. Seems like the forces would be equal but the "climb" right to left sure looked better.

My mill is an old Van Norman #12 with a fair amount of wear and I am inexperienced enough not to know what to expect from her yet. I believe my mill can only be adjusted or tramed in the Y axis the X axis is fixed.


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[6literZ]

If you mount an indicator to your spindle or mill head and indicate the face of the part you just cut you can move the y axis from top to bottom of the part. If you see the part is dished in the middle you have a head tram issue. If not bad, you could just have a feed rate issue or cutting edge geometry issue causing some rubbing and galling.

I recently spent some time on tram and setting the face mill insert height and it was nice to see good results.

 

[ddickey]

Start at 26:55

 

[mikey]

Mikey,

You are correct, typing error on my description, the second set of picks was RIGHT TO LEFT. Thanks for catching that.

I will give your suggestions a try. Thank you.

I'm still confused by the concept of climb vs conventional milling when the cutter is larger than the piece so it clears both edges. Seems like the forces would be equal but the "climb" right to left sure looked better.

My mill is an old Van Norman #12 with a fair amount of wear and I am inexperienced enough not to know what to expect from her yet. I believe my mill can only be adjusted or tramed in the Y axis the X axis is fixed.


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Thanks for clarifying, John. Yeah, climb cuts almost always look better, and with a big mill like yours (provided the ways and screws are tight), climb cuts for just about all cuts will work better. Still, it is usually better not to run the flycutter down the center because this alters chip formation/thickness. In a climb cut, the chip is supposed to thin as the cutter drives through the cut but when the cutter is running down the center it doesn't do this - it keeps cutting so you'll have greater wear. At least for me, I try to only extend the cutter on the far side of the cut (relative to the tool position) by 20% or so, and I do this for both conventional and climb cuts. Just empirically over time, this seems to result in the best finishes and tool life so that's my reasoning.

You might mess with speeds and feeds to see if that improves your finishes. Add that tiny nose radius to the tool and see if it helps.

EDIT: forgot to say that a flycutter has no gullet so the chips have no place to go until the tool exits the edge. Running off to the side of a narrow work piece allows better chip evacuation, I think. You have to see my Tormach Superfly cut aluminum to see what I mean. The chip flow is definitely directional and the finish improves if I run the tool off to the side.

 

[T Bredehoft]

I'm still confused by the concept of climb vs conventional milling when the cutter is larger than the piece so it clears both edges

I havent seen this adressed, You're right, climb/conventional only applies to the side of the (endmill) cutter, not a fly clutter.

 

[mikey]

Given that the concept of conventional vs climb milling addresses how the chip forms with each mode, I believe it also applies to a fly cutter. The edges doing the cutting differs between end mills and fly cutters but the same concepts should apply. Clearly, the finishes that result from each method differs, just as it does with an end mill.

 

[ddickey]

Did you watch the video? Climb and conventiional absolutely apply to fly cutters.