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View Full Version : Best Practices for Flycutting / Interrupted Cuts On Bridgeport



mattthegamer463
03-19-2018, 11:26 AM
I just got a proper mill and I'm interested in being kind to it as it has already lived far longer than I have. One thing I know is a tough job is interrupted cuts. My old mill/drill didn't have gears so I was probably just punishing the spindle spline, but from what I've learned so far the clutch dogs in the bridgeport style heads don't care for the beatings that interrupted cuts give.

Is there a way to do this best with minimal pummeling? entering the workpiece with the fly cutter set not right down the middle, but to the end of the part, to try to ease it into the work instead of punching the edge like a wall?

Using an insert face mill, ideally with enough inserts that it's always got contact with the part and then never interrupts?

Higher RPM, lower depth of cut? Low chip load I presume is good for it, so a higher RPM and a lower DOC with more passes would be nicer to it, albeit taking more time to accomplish the task.

I suppose I can perform the "see how it sounds" test and stick to the quieter methods.

old mart
03-19-2018, 01:42 PM
Milling is all interrupted cuts, but unless you are in a terrific hurry, then smaller cuts put much less strain on the machine. If you use solid carbide, then on a manual mill you can use maximum rpm as the cutters are designed for much higher speeds. A shell mill of up to 100mm diameter will have at least 5 tips, more likely 8, will spread the forces. I use a Ceratizit 50mm 5 round tipped shell mill for all types of steel, as it cuts easier and the tips can be indexed to 8 positions, so there are 16 edges per box. I think the Ceratizit is limited to about 11000 rpm as long as the screws are changed with the tips, so my max of about 2100 is not going to worry it.

Davek0974
03-19-2018, 02:53 PM
Smaller fly-cutters are ok I think - I cut several traction engine cylinder saddles on my old girl, thats a 12" dia cut using a single tip on an extension arm mounted on a large boring head, each saddle was about 10" deep so i used the quill and knee for the cut, happy days :)

Anyway she managed it OK and is still running today as a CNC mill, the splines and the dogs take a beating but seem like they always rattle anyway, certainly didn't get any worse, i always made sure she was well oiled, including the splines, maybe that helps?

garyhlucas
03-19-2018, 04:02 PM
I think the only reason for fly cutters to exist today is simply that they are the cheapest cutter available for a mill. In the old days of carbon steel cutters and very slow spindle speeds they were a good match. They can produce a nice looking finish.

If you want flat to the limits of your machines capability an end mill wins because it won’t deflect like a fly cutter. If you want the highest metal removal rate a solid endmill sized to use the spindle rpms available while maximizing the load on the motor will be fastest by far.

There is lots of talk about HSM High Speed Machining today. What most people don’t realize is that it is becoming popular is not so much that it faster cutting. It is because non-geared spindles are simple, cheap, and accurate, but don’t produce lots of torque and at 1/4 speed they put out 1/4 the power. So small tools turning at higher speeds match those spindles better, and use more of the available hp

MattiJ
03-19-2018, 05:09 PM
I think the only reason for fly cutters to exist today is simply that they are the cheapest cutter available for a mill. In the old days of carbon steel cutters and very slow spindle speeds they were a good match. They can produce a nice looking finish.


Another reason being that its much faster to take a one 12" wide cut on a manual machine vs. gazillion 1/2" cuts. Big fly cutter and carbide tooling is good match as you get enough high SFPM even with museum mills.

I don't know why the fly cutter is always envisioned as a bar sticking out of spindle.. make it solid disk and it won't deflect and the rotating mass helps with hammering.
https://youtu.be/reQxZOjaNaA

My "little giant" flycutter:
https://i.imgur.com/vU7P5e0h.jpg

754
03-19-2018, 05:19 PM
I think the only reason for fly cutters to exist today is simply that they are the cheapest cutter available for a mill. In the old days of carbon steel cutters and very slow spindle speeds they were a good match. They can produce a nice looking finish.

If you want flat to the limits of your machines capability an end mill wins because it won’t deflect like a fly cutter. If you want the highest metal removal rate a solid endmill sized to use the spindle rpms available while maximizing the load on the motor will be fastest by far.

There is lots of talk about HSM High Speed Machining today. What most people don’t realize is that it is becoming popular is not so much that it faster cutting. It is because non-geared spindles are simple, cheap, and accurate, but don’t produce lots of torque and at 1/4 speed they put out 1/4 the power. So small tools turning at higher speeds match those spindles better, and use more of the available hp

What are working on? And how many 6 to 10 inch face mills do you own?

BCRider
03-19-2018, 05:44 PM
Fly cutter or larger size insert face mill for a nice finish looks. Reasonable diameter end mill and multiple passes if you want a flatter and more true surface.

Now before that idea gets jumped on let me explain.....

If the mill is perfectly in tram, bearings are good and the mill does not flex then either can do just fine. But if things are out a touch on the tram then a flycutter or large face mill will cause a tilted or scooped cut depending on the tram error. And if out at some angle then both a scooped and tilted cut.

Now an end mill will do the same thing. But being a smaller span the error for any single pass is going to be very small. If a 4 inch flycutter on an out of tram setup produces a .0015 scoop in the middle of the cut then a 3/4" diameter end mill will only produce .75/4 x .0015=.0003 roughly.

The surface left from an end mill may not be as pretty to look at but if the need is more for flatness then that's how I tend to go.

It's also not any slower. In fact Guy Lautard wrote an article in one of the Machinist's bedside readers comparing the two. The flycutter has to cut at a lower RPM. Plus it only has one cutter so the feed rate has to reflect that or the chip load goes up. On the other hand a 4 flute end mill running at the same SFPM and chip load is going to speed through each pass at a far faster rate.

Also if the mill is in perfect tram the flycutter has an advancing line and a trailing line in the cut. And it needs to feed onto the part and off the other end for a little over half the diameter on each end at the same glacial feed rate to keep that pattern looking good. The end mill needs that same treatment. But with the multiple teeth and matching feed rate it is moving faster and has less distance to travel.

Bottom line was that a "by the numbers" comparison between something like a 3" flycutter with HSS and a .5" HSS end mill on a 2" wide bar was that the end mill was actually faster. But I can say from personal trials of both that the flycutter when set up just right leaves a really nice looking surface which the end mill can't match by a country mile.

Back to your question. I would not worry about it. Mills are designed and made knowing that much of the cutting done on them is going to be interrupted cuts. And it's not like you hog off yards of metal with a flycutter. That's what insert shell mill cutters are for. To speed things up though do use a screw insert style tool or a brazed insert tool so you can up the RPM to a value that is a little more reasonable. And since it is a "one tooth wonder" if you find the trailing sweep is cutting deeply instead of just tracing a line then by all means switch corners. And when the corners are all used hone it with a diamond slip if you don't have a new insert. A flycutter is only to be used for lighter cuts anyway. I'd never think of taking off more than probably .005. If I need to cut things down by as much as .010 then I'm switching to an end mill to hog the majority of it away and leave the last .002 to .005 for the flycutter.

It would also be a mistake to use too light a feed. That's a great way to rub the cutting edge into dullness. You want to see little curlies coming off as actual chips. If you're just getting dust then speed up the traverse a touch. You certainly don't want to see big blue coarse chips either but the edge needs to get into the material and form an actual chip. I find that when things are running neatly that the sound the cutter makes is a light bump with a little short sizzle sound.

MattiJ
03-19-2018, 06:04 PM
flycutter is only to be used for lighter cuts anyway. I'd never think of taking off more than probably .005. If I need to cut things down by as much as .010 then I'm switching to an end mill to hog the majority of it away and leave the last .002 to .005 for the flycutter.


My Aciera F1 is totally spindle power limited with fly cutter (no real suprise there) but it was easy also to push a 2500lbs russian toolroom mill to max power with disk style carbide flycutter. Chips fly f**** everywhere when you push 8" fly cutter at 900 sfpm and 1/8" DOC.
Sounds nasty but the russian tools are always designed for hammering&sickle duty ;)

tomato coupe
03-19-2018, 06:19 PM
I don't know why the fly cutter is always envisioned as a bar sticking out of spindle.. make it solid disk and it won't deflect and the rotating mass helps with hammering.


A bar is simple. Once you add a solid disc, you may as well add more inserts and make it a face mill.

754
03-19-2018, 06:25 PM
One thing about flycutting, you can choose the finish you Want or Need.
Flatness is relative.. in engine resurfacing the cutter is intentionally out ofmtram, at least 1/2 thou in a foot.so it cuts a not flat surface but adequate for intended use..

JoeLee
03-19-2018, 06:26 PM
What I've found is when ever you have an interrupted cut your setting up a vibration pattern that will show up in your surface finish.
I use a Bison 5" shell mill with one carbide insert for my bigger fly cutting jobs. As massive as that head is for my BP and even with .005 DOC and varying the R's I still got a pattern from vibration. It started where the insert met the work and gradually faded away to a perfect finish just before the insert exited the work surface.

JL...............

mattthegamer463
03-19-2018, 09:43 PM
Thanks for the insights. I've been using a small fly cutter with HSS and later a TCMT and round insert holders I made, which work pretty well and hold an edge much better. The glacial pace as mentioned is a pain. I built a power feed for the mill drill just to help that.

I just ordered an import 6 insert face mill to try, at least it can be fed at a more reasonable rate and should give a nice finish with purpose-designed inserts instead of the triangle and round types which seem to need just the right feed rate to leave a nice surface.

I feel I'll be planning another power feed design pretty soon.

Sent from my SM-G930W8 using Tapatalk

lakeside53
03-19-2018, 10:26 PM
It's not the dog clutch that take the heat; if that's adjusted correctly and not in bad shape, it "locks" well. The dog clutch still drives splines. Both the male and female splines wear. The female is part of the lower dog clutch part. The male (spindle) can easily be tested by trying it at full extension verses the middle or close in. You can hear the difference.

But.. Just ignore it. Make chips. If it wears out, fix it.

dian
03-20-2018, 05:24 AM
One thing about flycutting, you can choose the finish you Want or Need.
Flatness is relative.. in engine resurfacing the cutter is intentionally out ofmtram, at least 1/2 thou in a foot.so it cuts a not flat surface but adequate for intended use..

intentionally out of tram? why would that be and how will you hold the tolerance?

EVguru
03-20-2018, 06:03 AM
You can put a drag on the spindle to keep the quill splines loaded. I did it once with an Aluminium disk and a couple of hard drive head magnets.

I've seen it done with a set of vanes driven from the end of the drawbar.

sandiapaul
03-20-2018, 06:11 AM
Get yourself one of these:

https://www.youtube.com/watch?v=Y2Xa0PMHM1U

I have probably a half dozen flycutters, some homemade and some commercial, the superfly blows them all out of the water. BTW, I use them on manual machines as well as cnc the equal effect.

old mart
03-20-2018, 10:27 AM
Is there a way of balancing in the design of flycutters?

Mcgyver
03-20-2018, 10:41 AM
best practices?

- use the right size fly cutter. To large for the work and you have to run it more slowly than it needs to be

- have it enter at close to a tangent - minimized pounding

- grind the cutter properly!! Very often I see people use the equivalent of a knife tool when what it requires is a facing tool. Think through the tool geometry, where the cutting edge is, direction of cut and where the rake is - a knife tool shape is what you want for boring, i.e. plunging, not fly cutting. Like facing with a knife tool in the lathe, it will work, but its not optimal or a best practice.....here's my go to facing tool, lots of rake established by a chip breaker. Use the same grind in a fly cutter for best performance.

https://i.imgur.com/QlNEfyX.jpg

Rich Carlstedt
03-20-2018, 11:13 AM
As Paul said in post 15, you want to have a slight drag on the spindle which protects the spline on the spindle and does not pound it

A quick and easy method ( and cheap !) used by old timers was to place a wine cork against the spindle nose using the indicator clamp hole on the right side of the Bridgeport Head for mounting.

Also use your knee for Z moves with the quill full retracted.


Rich

For Clarity:
Using a "L" shaped 1/4 rod, they drill a 3/16 hole through the cork and forced the rod through it and then swung it into position. I am sure lunch was a fun time as the bottle could not be plugged after ...

BCRider
03-20-2018, 11:50 AM
T.....I just ordered an import 6 insert face mill to try, at least it can be fed at a more reasonable rate and should give a nice finish with purpose-designed inserts instead of the triangle and round types which seem to need just the right feed rate to leave a nice surface......

Someone above mentioned about the power needs if you're removing that much stock. You didn't say what size mill you bought but it's quite possible that the higher load you can produce with a 6 tooth cutter will bog the machine down when fed at the rate for the best finish. I'll be very interested in reading your results.

If you find that the poor mill isn't happy with pushing 6 teeth through a wide cut there is an option though. Remove three of the teeth so only one is taking the big cut across the middle and when two are engaged it is on the entry and exit. Not only will this reduce the load on the motor but it should smooth up the interruptions. And if that still proves to be too much go for two opposed teeth so it's still only one tooth at a time in the cut. But at least with something like that you've got options.

The only downside of a large face mill of that sort is that it's a fixed diameter setup. Mind you I can't see this being a big deal. I'd think that a couple of sizes and any of us home shop types would/should consider ourselves well set up.

old mart
03-20-2018, 01:00 PM
A six tip shell mill has even more versatility than BCRider says, it will still be balanced with 4 tips and even with only one tip, the out of balance forces will be less than a fly cutter.

JoeLee
03-20-2018, 01:14 PM
I'll bet it puts a nice polish on the spindle nose after a while.

JL................

mattthegamer463
03-20-2018, 02:12 PM
That tip about removing inserts is a great idea, there's nothing saying the cutter needs all six installed. I am pretty excited to see how it works out.

The new mill is a Bridgeport clone so it should be able to eat up material pretty well. Won't be carving out engine blocks from billet (not that I would be anyway) but it's going to be heaven compared to 10 minute passes with the fly cutter and mill drill.

RB211
03-20-2018, 02:17 PM
I just picked up one of these and love it. It cleaned the mill scale right off some HRS and made it look like tool steel.
https://www.amazon.com/gp/aw/d/B00PWCYLSI/ref=mp_s_a_1_16?ie=UTF8&qid=1521569707&sr=8-16-spons&pi=AC_SX236_SY340_QL65&keywords=indexable+endmill&psc=1


Sent from my iPhone using Tapatalk Pro

tomato coupe
03-20-2018, 02:24 PM
That tip about removing inserts is a great idea, there's nothing saying the cutter needs all six installed. I am pretty excited to see how it works out.

The new mill is a Bridgeport clone so it should be able to eat up material pretty well. Won't be carving out engine blocks from billet (not that I would be anyway) but it's going to be heaven compared to 10 minute passes with the fly cutter and mill drill.

I bought a 5" eight-insert face mill many years ago when I had a Bridgeport, with the same idea that I could remove inserts if I needed to. In reality, however, I never had to do so.

BCRider
03-20-2018, 04:09 PM
TC, what HP motor is in your BP? I'm running one of the smaller knee mills so I've got a whopping 1.5HP running on 220v single phase.

Another question for those that have used the big facing cutters that fit onto separate shell mill arbors. Like THIS STYLE (http://www.shars.com/products/indexable-cutting/indexable-milling/4-indexable-coolant-thru-45-degree-face-mill-seht-insert) on THIS ARBOR (http://www.shars.com/r8-1-1-2-face-shell-mill-tool-holder) Did you find that the cutters all zero up well? I'm wondering if I should look at an arbor and then a couple of sizes of that style in something like 3" and 5" to cover all my needs.

tomato coupe
03-20-2018, 05:22 PM
TC, what HP motor is in your BP? I'm running one of the smaller knee mills so I've got a whopping 1.5HP running on 220v single phase.

I don't have that machine anymore, but it had a 3 HP motor on it. I ran it from single phase 220 V using a static phase convertor, however, so it was effectively more like 2 HP.


Another question for those that have used the big facing cutters that fit onto separate shell mill arbors. Like THIS STYLE (http://www.shars.com/products/indexable-cutting/indexable-milling/4-indexable-coolant-thru-45-degree-face-mill-seht-insert) on THIS ARBOR (http://www.shars.com/r8-1-1-2-face-shell-mill-tool-holder) Did you find that the cutters all zero up well? I'm wondering if I should look at an arbor and then a couple of sizes of that style in something like 3" and 5" to cover all my needs.

Are you asking about the variation in height of the inserts compared to each other? I think that would be highly dependent on the quality of the face mill. (My face mills are of medium quality and the inserts are within a .001" range.)

BCRider
03-20-2018, 07:11 PM
That helps. But really the whole idea of how any variations stack up due to the large face diameter and consistency on the shoulder of the arbor. Or are you saying that when assembled and running that the max variation is around a thou?

tomato coupe
03-20-2018, 07:35 PM
That helps. But really the whole idea of how any variations stack up due to the large face diameter and consistency on the shoulder of the arbor. Or are you saying that when assembled and running that the max variation is around a thou?

Yes, but I thought you were asking about the height variation of the inserts due to how they sit in their respective pockets. My present setup consists of medium quality 2.5" and 5" face mills on higher quality CAT40 arbors. I don't see any indication of the face mills being out of alignment with the arbor, just some small (<.001") random height variation between inserts.