Looking For a Better Way to Make This

[rgrin]

I have another production order for one of our more tight tolerance parts.  The customer is getting closer to their final design and is of course forecasting "HUGE" order volumes.  I am personally not sure of that, but I am looking at our process with that in mind.  This new order is large enough to justify retooling/reprocessing.

I made a dummy model to represent the trickiest features to get right. 

Dimensions in Inches. Part Material is 7075. Machine making it is a Yasda H40i in a thermally isolated room.

Previously I surfaced Datum A-B and then rotated 90 and milled the red parts.  This is when we discovered how big of a pain thermal drift is when going from High RPM surfacing to low RPM finishing.  I was fighting the position of A-B as the tool would grow and thermal comp wouldn't keep up.

I have been thinking of trying a large inserted slot mill to machine the datums while the machine is at 90.  I found that Ingersoll and Seco (and I am sure others) make ones with honed and polished inserts.  The issue I ran into is I could not find a Big Plus BT40 holder compatible with the tools I was looking at that was also long enough to clear the 8.75" dimension.  The machine can accept up to 4" Diameter tool at 11.75" long and weighing 15 pounds.  I'm wondering if I would have to ask Big Daishowa to make me a custom one?  I just lack the conviction that the slot cutter would be free enough cutting at that gauge length to start that path.

 

Any insights appreciated

[crazy^millman]

Flat endmill using a multi Axis toolpath to cut them. the slot tool is going to introduce too much stress into the part. Might use a 3/8 endmill to reduce the tool pressure also, Develop the process and make sure you are roughing to a plus condition. Let normalize for 24 hours or use dry ice for 4-6 hours. Semi Finish to still a plus condition then repeat the 24 hour or dry ice normalization then finish.

[rgrin]

22 minutes ago, crazy^millman said:

Flat endmill using a multi Axis toolpath to cut them. 

The part goes through 2 Roughing and 2 Semi finishing operations prior to the finishing operations.

Previously I tried using a flat endmill when we were first experimenting and I could not get it to cut right.  I was using a 3 Flute 3/16" Uncoated endmill from SwiftCarb that I use for finishing other parts.  I think it was dragging weird on the flat of the tool and leaving awful stepover lines.  I was using a swarf path. I remember trying to keep the centerline of the tool pointed at the diameter, but maybe that was the wrong thing to do?  Maybe a different endmill would work better?

 

[Kyle F]

10 minutes ago, rgrin said:

The part goes through 2 Roughing and 2 Semi finishing operations prior to the finishing operations.

Previously I tried using a flat endmill when we were first experimenting and I could not get it to cut right.  I was using a 3 Flute 3/16" Uncoated endmill from SwiftCarb that I use for finishing other parts.  I think it was dragging weird on the flat of the tool and leaving awful stepover lines.  I was using a swarf path. I remember trying to keep the centerline of the tool pointed at the diameter, but maybe that was the wrong thing to do?  Maybe a different endmill would work better?

 

They make true flat bottom endmills, that would work perfectly for this. without that negative rake towards the center of the tool. 

Funnily enough, I learned about this during CamInstructor's RON WEEK videos haha! how fitting 

[rgrin]

8 minutes ago, Kyle F said:

They make true flat bottom endmills, that would work perfectly for this. without that negative rake towards the center of the tool. 

Funnily enough, I learned about this during CamInstructor's RON WEEK videos haha! how fitting 

If that is all I needed, imma be pretty upset. I thought about looking for those, but we just did not have enough time.

 

Do you have any you recommend? 

[Kyle F]

30 minutes ago, rgrin said:

If that is all I needed, imma be pretty upset. I thought about looking for those, but we just did not have enough time.

 

Do you have any you recommend? 

sandvik coromill plura, when you're filtering endmills on their website you can specify by "centre cutting capability"

 

 

https://www.sandvik.coromant.com/en-us/knowledge/milling/turn-milling

I would maybe shoot them an email and double check but I believe true flat bottom is CCC....

If true flat bottom is too hard to find I suppose you could do a .375 inserted cutter

 

https://www.tungstentoolworks.com/products/end-mill.asp#

Or you could order custom from TTW

 

[AMCNitro]

Why not make a fixture for the lathe with the "V" shape of the bottom, the part can slide into it?  Sorry if I'm missing something

[rgrin]

16 minutes ago, AMCNitro said:

Why not make a fixture for the lathe with the "V" shape of the bottom, the part can slide into it?  Sorry if I'm missing something

Any variation on the Vs would twist the part while clamping and likely throw the part out of tolerance after releasing.  I didn't model it, but we have tooling lugs on both sides that we fixture with. They get remachined flat prior to the finishing operations.

[rgrin]

28 minutes ago, Kyle F said:

If true flat bottom is too hard to find I suppose you could do a .375 inserted cutter

I'll keep the Plura line in mind.

Those TTWs look interesting.  Website is quoting $70 per for 4 3/8" endmills. Not terrible

Why would an insert cutter work if a regular endmill doesn't? Trying to wrap my head around it.

[crazy^millman]

43 minutes ago, rgrin said:

I'll keep the Plura line in mind.

Those TTWs look interesting.  Website is quoting $70 per for 4 3/8" endmills. Not terrible

Why would an insert cutter work if a regular endmill doesn't? Trying to wrap my head around it.

No most insert cutters are not flat bottom bY design. A flat bottom endmill is the correct call here in my humble opinion.

[Kyle F]

53 minutes ago, rgrin said:

I'll keep the Plura line in mind.

Those TTWs look interesting.  Website is quoting $70 per for 4 3/8" endmills. Not terrible

Why would an insert cutter work if a regular endmill doesn't? Trying to wrap my head around it.

I personally would go with TTW to guarantee the true flat bottom.

After thinking about it,.. and trying to wrap my own head around it,.. I found this on sandvik's turn milling link.
an insert cutter would be great for something like turn milling on a 4th axis though assuming they're the right geometry inserts.

 

[cruzila]

Some of new grinds on regular endmills have a wiper feature. With a flat bottom EM the center never really rurns that fast and could cause finishes to not be good.

With an EM with a wiper, the offest theory would work and provide a nice sharp corner.

Admittedly I have no experience with new fancy flat EM like that, except we used to grind them for cbores back in the day.

[rgrin]

38 minutes ago, cruzila said:

Some of new grinds on regular endmills have a wiper feature. With a flat bottom EM the center never really rurns that fast and could cause finishes to not be good.

The SwiftCarb endmill that I tried it with previously is stated to have a wiper

[Jasond0530]

I've used these for that exact feature. worked well although cutting force wasn't considered.

used an endmill for the walls first.

ADF | Drills | PRODUCTS｜OSG

 

[JB7280]

7 hours ago, Jasond0530 said:

I've used these for that exact feature. worked well although cutting force wasn't considered.

used an endmill for the walls first.

ADF | Drills | PRODUCTS｜OSG

 

What am I missing here?  You used a flat bottom drill, to mill a slot?

[Johnward Holmeson]

19 hours ago, JB7280 said:

What am I missing here?  You used a flat bottom drill, to mill a slot?

Sounds like they milled the walls first leaving stock on the floor, and used the flat bottom drill to finish the floor.  Interesting.

[JB7280]

1 hour ago, Johnward Holmeson said:

Sounds like they milled the walls first leaving stock on the floor, and used the flat bottom drill to finish the floor.  Interesting.

That's what it sounds like to me, but I wouldn't think a flat bottom drill would cut like that.  Maybe because the corners of the tool never touch?

[AHarrison1]

16 minutes ago, JB7280 said:

That's what it sounds like to me, but I wouldn't think a flat bottom drill would cut like that.  Maybe because the corners of the tool never touch?

I don't see a problem with using that tool. The carbide nature of the tool should give it the rigidity needed although I would think the length

would be no more than 3D