fly cutter or face mill

[Martin Shaw 1Participant @martinshaw1]

I am making some clamps for the machine vice which involves starting with a piece of steel 30mm by 20mm, reducing the smaller dimension to 18.8, and then creating wide rebates on two faces. I have tried mutliple passes of a 12mm cutter, which didn't turn out too well, and logic prompted the realisation that the cut in a single pass is the best way. The title gives my thinking, a fly cutter with a HSS tool will undoubtedly be a bit cheaper but the offside is the resharpening of the bit by grinding which I'm not good at. By contrast a carbide insert face mill will cost a bit more initially but there is a lot less grief to reach the end, however other views are always welcome to aid the decision making process, any thoughts?

Regards

Martin

[Martin Shaw 1Participant @martinshaw1]

[Andy CarruthersParticipant @andycarruthers33275]

What speed are you running the (presumably) HSS cutter at?

How deep are your cuts?

I had problems with TC tools as I was running too slow, TC should be (roughly) twice the speed of HSS

[JasonBModerator @jasonb]

Even though I have a 50mm facemill I still tend to use a flycutter for 98% of sizing up stock. Only really get the facemill out if it's an iron casting that may have some hard spots in it which blunts the HSS.

Most of the time I will use the middle size from a set like this with a 6mm toolbit, not to hard to grind yourself ( see Milling for beginners) or ARC will sell you a preground bit. Works out very cost efficient as a bit will take many touch ups. Similar flycutter is easy enough to make, I think Ron made one.

On your SX2.7 I would suggest two passes to get to your required size, ideally one each off opposite faces, about 800rpm if using that size flycutter which will be swinging 35-40mm at the tip.

With the 12mm cutter you should only need 3 or 4 passes 10-7.5mm wide on each at the full 1.2mm deep.

Edited By JasonB on 08/05/2019 14:49:22

Edited By JasonB on 08/05/2019 14:50:54

[pgk pgkParticipant @pgkpgk17461]

A simple compromise is to make a flycutter with a carbide tip. You should find pics on the web. My own version was simply made with a round carbide insert thus simple rotation if I fear it's blunting or chipped. I do still use HSS flycutters but more on ally than steel where the finish is often mirror-like. the carbide I tend to use when i can skim the surface without leaving it i.e avoid the risk of chipping or any dropping of the flycutter arm as it leaves the surface (down to the rigidity of flycutter arm)
The obvious benefit of carbide is the speed of rotation on a larger item when hand-winding it.

pgk

[Martin Shaw 1Participant @martinshaw1]

Right, in answer to some questions I was cutting at 400rpm, which appears to be too slow, and with a v small DOC just to see what the finish was like. I have put a pic below, pretty it ain't, and I do wonder whether the cutter is a bit blunt. There are distinct ridges between the passes which certainly shouldn't be there. I have never used either a fly cutter or a face mill so I'm well in the dark, but from Jason's comment it seems a fly cutter is the first choice.

Regards

Martin

[Douglas JohnstonParticipant @douglasjohnston98463]

Looks like a blunt cutter to me or poor chip clearance. Poor tramming of the mill can also give this result where a trailing edge messes up the finish.

Doug

[Anonymous]

Hmmm, looks like the sort of finish you can get on hot rolled steel if the parameters aren't correct. To add to the parameters from Douglas I'd add feedrate. You need the cutter to cut not rub. I'd run the full depth in one go with a chip load of 0.1mm per edge. To summarise:

1. Check the tram of the mill

2. Make sure cutter isn't blunt

3. Run at a sensible spindle speed and feedrate

4. Brush the swarf away – if you're running fast 'n' furious the swarf tends to get thrown away, which helps

Andrew

[Martin Shaw 1Participant @martinshaw1]

Thanks guys, I think tomorrow I will try again with a new 4 flute cutter, up the revs and see if I can work out the feed rate that will give me the correct chip load. I'll let you all see the outcome. I think one of the learning curves beginners have is an acceptance that cutters are consumables and don't last for ever.

Regards

Martin

[JasonBModerator @jasonb]

Feed rate is revs x number of flutes x chip load so say 800rpm x 4 flutes x 0.1mm = 320mm/min or about two and a half turns of teh handwheel per second.

I have found the 2.7 likes a lower chip load, this is somewhere around 120-150mm/min.

[David George 1Participant @davidgeorge1]

Hi Martin this is the fly cutter that I use it has a solid tungsten carbide piece as the actual cutter.

It has a 12mm diamiter shank and a 25mm diamiter body with a grub screw to hold the carbide in an angled hole easy to make. If you like I have a spare carbide piece you could have to make your own. You can run it at a fast speed and get a lovely finish and little or no wear on the cutter. Send me a PM if you want me to send the carbide.

David

[Anonymous]

Posted by Martin Shaw 1 on 08/05/2019 19:53:15:

I think one of the learning curves beginners have is an acceptance that cutters are consumables and don't last for ever.

That's a very important lesson, and one which isn't always understood.

Andrew

[John HaineParticipant @johnhaine32865]

…but to protect them they are run too slow with no enough DOC so they rub and get blunt…

[JasonBModerator @jasonb]

Posted by Martin Shaw 1 on 08/05/2019 19:53:15:

I think one of the learning curves beginners have is an acceptance that cutters are consumables and don't last for ever.

This is where the flycutter pays off over endmills for the type of work described. I have had the same tool bit in my commonly used flycutter body for several years yet it probably gets sharpened every week or two depending on what I'm working on. Most beginners will certainly not have a means to sharpen milling cutters but most will have a basic bench grinder which is all that I use, no need for fancy rests that take 6months to make.

Also on a job like this where there is not much to come off the stock you can't take a decent DOC so end up just using the very corners of the milling cutter which soon wear and it gets put into the draw for edge work only. The fly cutter is happiest taking cuts upto 1mm deep and that worn end can easily be returned to sharpness with the added bonus that you can cover the work in one pass rather than going back and forth which saves time, screw/nut wear and if you get it right a nicer looking surface without overlapping pass marks.

[Ron LadenParticipant @ronladen17547]

In my limited experience I am a big fan of the flycutter, as Jason mentioned I made my own which was very easy to do. I got a HSS bit from ARC which made life easy as all the angles are there so its easy to maintain them when grinding a new edge. I like the finish the flycutter gives and depending on size it can be done in one pass, I have found that running a little faster than what the figures give seems to work well or at least thats what I,ve found.

The one I made:

[Martin Shaw 1Participant @martinshaw1]

Firstly my thanks to David for his kind and generous offer, and to both Jason and Ron for the additional information. I have decided to order from Arc a fly cutter, I know in the spirit of things I should make it, however by the time I've trolled around gathering materials etc and time which does have a cost if not directly financial, I will have spent at least as much. Once I have received it and had a go I'll report success or otherwise.

Many thanks

Martin

Edited By Martin Shaw 1 on 09/05/2019 11:19:58

[Martin Shaw 1Participant @martinshaw1]

Arc delivered to me a 2.5" flycutter and a pre ground HSS cutter, so thought I should try it out. Obviously never having used one before I didn't expect perfection however as you can see from the pic it is several hundred percent better than the first effort. I cut at 570rpm, a doc of 20 thou, and a fairly conservative feed rate, and whilst it's not glass and the tool marks are feelable it would suffice if surface finish wasn't critical, it isn't. I will do the other side at a slightly faster rpm to see whether that finesses the finish.The chips were definitely hot and tending towards blue, does this indicate the feed rate is still too high? A huge step forward nonetheless.

Regards

Martin

[JasonBModerator @jasonb]

Colour of the chips is probably more to do with cutting speed rather than feed.

As slower feed rate will make the gap between each cut smaller so you will get a smoother cut the slower you feed.

You can also get a smoother finish with a slightly rounded tip as the ones from ARC are angular, have a go at grinding the other end of the tool to match the preground one but just round the corner that is lowest, only needs a vert small radius that can be stoned on..

[Martin Shaw 1Participant @martinshaw1]

Thanks Jason, I'll give it a try tomorrow.

Regards

Martin

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