Flycutter help

[Anonymous]

Posted by SillyOldDuffer on 06/06/2018 16:33:22:

I have a WM18 squeezed into my garage. I think it's big. A Bridgeport is about 4 times heavier and I've seen them criticised by power users for being flimsy. I suppose it depends on what you're used to!

I wouldn't say a Bridgeport is flimsy, but it's certainly flexible, in at least two senses of the word. I've knocked it slightly out of tram by running cutters hard. I wouldn't run the flycutter as shown in the OP on my Bridgeport. In fact I wouldn't run one at all. I never seem to get as good a finish as I can get with an endmill. And the endmill leaves a flatter surface.

Now on the horizontal mill, for producing curved surfaces, it's a different matter:

With a DOC of 2mm and a feed of 0.2mm per rev there was no hint of vibration, and the mill didn't even cough. But it does weigh about 1700kg, even though the X/Y travels are slightly less than a WM18.

Andrew

[ChrisBParticipant @chrisb35596]

Posted by JasonB on 06/06/2018 12:05:30:

Stick the dti on your table and run it along in the x-x direction both without the vice on the table and also with the vice to one end as you have it in your photo.

Could be table is tilting/sagging or not running parallel even though it trams 0-0 with an empty table in the central position.

So I put the dti in the spindle and checked the table, set zero at full right travel and traversed the table to the left. I got -0.08mm on the far side.

This would explain why I got the dished face. Half way travel I had a difference of -0.06mm and that is the exact amount of dishing I measured on the test cut.

My next question would be, is it possible to adjust the table?

[John ReeseParticipant @johnreese12848]

It looks like a TNGA insert. That will increase the cutting forces compared with a positive rake insert. Try a TNMG insert to reduce the cutting forces. I have a full sized Bridgeport clone. To use a cutter like yours I would first need to tram the head. Then I would limit myself to very light cuts so the cutting forces would not knock the head out of tram. Your workmanship on the cutter is great. Unfortunately it is probably too much cutter for your machine.

[JasonBModerator @jasonb]

Looks like the insert is mounted at an angle which would give it positive rake.

Can't think of an easy way to adjust the table but when you have a job like this then tightening the gib strips may well help, if you have been using it for the last 18months or so like that without issue then probably not worth delving deeper into it.

[ChrisBParticipant @chrisb35596]

Posted by John Reese on 06/06/2018 23:41:06:

It looks like a TNGA insert. That will increase the cutting forces compared with a positive rake insert. Try a TNMG insert to reduce the cutting forces.

Yes its a TNGA, and it's not really meant for the flycutter as its CBN, I wanted those inserts for another project. I have some TNMGs on order but still not arrived yet, so that might help with the finish.

I'll have a go with some of the suggestions on here and see how it goes from there.

[SillyOldDufferModerator @sillyoldduffer]

Posted by John Reese on 06/06/2018 23:41:06:

… I have a full sized Bridgeport clone. To use a cutter like yours I would first need to tram the head. Then I would limit myself to very light cuts so the cutting forces would not knock the head out of tram. …

That sparked a thought – I think the design of the WM18 family increases the chance of knocking the head out of tram compared with many bigger machines. To tilt the cutter on this type of mill, either to deliberately cut at an angle, or to set it true, the whole head swivels on an axle bolt. A second bolt clamps the head assembly to the body, keeping the head firmly in position.

This is a straightforward and effective design except bolted parts always face some risk of an unexpectedly sharp blow shifting the alignment slightly. The risk is zero when drilling, minimal with fluted cutters, and I guess typical flycutting is also safe because it applies front-back forces across a narrow strip rather than risky right-left blows.

Another point – my WM18 flycutter is much lighter than Chris's. Not only is the energy stored in the tool much lower, it has spring in the construction that tends to soften shocks. Chris' super-flycutter will store a lot more energy and it's rigid construction is likely to transfer blows straight on to the spindle and perhaps hammer the head alignment. I suppose it's even possible that the tram of a WM18-type mill might be nudged to and fro as the heavy tool bites on each turn.

A good idea to check tram after any kind of bump or unusual vibration.

Dave

[ChrisBParticipant @chrisb35596]

Posted by SillyOldDuffer on 07/06/2018 10:48:42:

Another point – my WM18 flycutter is much lighter than Chris's. Not only is the energy stored in the tool much lower, it has spring in the construction that tends to soften shocks. Chris' super-flycutter will store a lot more energy and it's rigid construction is likely to transfer blows straight on to the spindle and perhaps hammer the head alignment. I suppose it's even possible that the tram of a WM18-type mill might be nudged to and fro as the heavy tool bites on each turn.

A good idea to check tram after any kind of bump or unusual vibration.

Dave

OK,OK…maybe I miscalculated a little bit and it came out slightly on the larger side But point taken, will make another shorter bar for it to reduce the vibrations etc.

Regarding the head getting out of tram, if I had to fit a couple of stops ( similar to the adjusting bracket on the RH side of the head but a little beefier ) , that should stop the head from moving accidentally….or not?

This morning I gave it another try -trammed the head again, then reduced the swing to 2.5" (that's the shortest it will go) and rotated the work piece by 90 deg and lowered the speed at 170rpm as suggested yesterday. I only did a single pass with one side of the cutter not both…Good result! Finish was definitely better and after checking for flatness I found it was pretty close, a 0.02mm feeler would not slide in .

Something else I noticed while checking the table for flatness was that from the right edge up to two thirds of the table the dti reads 0, then from 2/3 of the table to the left edge it starts reading off. I trammed the head on the flat part of the table and set the vice on this side. Will try increasing the swing on the fly cutter and see what happens.

[SillyOldDufferModerator @sillyoldduffer]

That's a good result Chris, and it suggests the main cause of your original trouble was simply expecting a little too much of the mill. A case of Scanderbeg's sword needing Scanderbeg's arm. I don't see the tool as any kind of failure; on a bigger mill I expect it would perform without fuss.

I'm not sure putting stops on the mill to stop it getting nudged out of tram is a good idea. When energy is dumped into the body of a machine it has to go somewhere. Increasing the weight, strength and layout of the machine itself is the best way of dealing with it.

In the absence of weight in a WM18, allowing the tram to move is quite a good way of dissipating energy without breaking anything. If you fit stops, the shocks might hammer expensive bearings instead, or even crack the frame. Or the WM18 might be strong enough to cope.

As amateurs we don't have access to design detail and, without knowledge, can only have hazy notions as to how strong, or not, a machine is. For example, plastic gears used in small mill for cheapness alone would be bad, and it makes sense to replace them with metal. On the other hand, plastic gears may be installed as a fuse so they break before something more expensive. If that's the case it's daft to replace them. As I don't know what the designer intended, or have access to the stress calculations, anything I say is a guess.

One of the nice things about Chinese kit is that it's not so expensive and lovable that I'm afraid to take risks and make modifications. In your position I'd certainly try fitting stops, but there would be no tears if doing so broke it.

Dave

[John ReeseParticipant @johnreese12848]

Chris,

Reducing the swing of the cutter was indeed a good idea. I suggest leaving the "tail" of the bar long enough to work as a counterbalance. With the tool balanced you should be able to increase your RPMs to get about 600 sfm at the insert. Most modern carbides are rated for such speeds. That should give you a near mirror surface. Depth of cut and feedrate will depend on the rigidity of your machine.

When I was lead in the machine shop many complained that all I wanted to do was turn up the speeds and feeds. Yes. I was trying to get the maximum performance out of each machine to improve profitability. In the hobby environment I still try to maximize my metal removal rate. I realize I shorten tool life bu with the price of carbide from China that is not an issue. Besides, over the years I acquired a few hundred various inserts. I doubt I can use them up in this lifetime.

Don't be afraid to try higher speeds and feeds and depths of cut. That is the only way you can determine the limitations of your equipment. I have watched a number of You Tube videos showing milling machine being run too slow in both RPM and feedrate. Depths of cut were far less than the machine and tool were capable of. That caused excess tool wear from rubbing as well as increasing the time to do the job.

There are time, of course, when you need to be extremely conservative in speeds and feeds. A good example of that is the machining of an expensive engine casting.

I was surprised that your initial cut was from left to right. That had the hot chips flying at you. It is much nicer to cut the other way and have the hot chips flying away from you.

[ChrisBParticipant @chrisb35596]

I'll leave it as it is for now as it's working fine, then if it gets out of alignment I'll consider adding stops. I made the fly cutter that size thinking I want to cover the width of the table with one pass for that odd job ( the only thing I can think of right now would be facing a cylinder head for example) I can easily make a short inset holder bar for small work, and that will be my next project – than I can crank up a bit on the rpm and see how it goes.

Thanks for all the advice and tips, gents – much appreciated

Edited By ChrisB on 07/06/2018 22:39:36

[Author]

Posts