The slower feed rate will mean that each tip cuts the metal more times for the same given spindle speed so you may only be using two inserts but they are cutting twice as much so will wear faster.

For example using some simple numbers. 1000rpm and feed of 400mm/min with a 4 insert cutter gives a chip load of 0.1mm so to cut a 400mm long piece of work each tip cuts 1000 times at 0.1mm each cut.

1000rpm and feed of 200mm/min with just two inserts also gives the same chip load of 0.1mm but to cut that same 400mm piece of work each tip cuts 2000 times at 0.1mm each cut so twice the wear on the two inserts.

And don't even think of using a fly cutter.

Regards Ian.

Yep, I still use my flycutters quite a bit, any specific reason they should not be used Ian?

I have a couple of industrial quality indexable tip milling cutters,I use them very often with a single insert tip,I use hss flycutters which will produce better finishes ,they are far cheaper and easier to change rake and profile by hand grinding,I even have some expensive artificial diamond insert tips which I used for flycutting ali cylinder heads, they were a gift,its just horses for courses, Though why spend lots of cash on inserts when HSS very often gives better results on the lighter machines used with our hobby. When I started with a ML7& and vertical slide,in the 1960s I did not buy milling cutters ,for all flat faces I used an assortment of home made fly cutters and used worn out hss centre drills as tool bits, and scrounged slot and endmills where slots and grooves were needed,as you progress in engineering, contacts are useful for supplies, and now when I am getting too old,i get more messages "" got a load of tools/ cutters etc do you want them for free" .Redundancy is also beneficial at times lots of usefull stuff can be aquired.

Gary posts what he thinks is a frugal observation to save a couple of inserts which for a MODEL INGINEER seems a good saving on the pocket and then receives a "Tecky" explanation of what he's doing wrong and even though it's a balanced assembly with two cutting faces , I remark, tongue in cheek, the "Folly" of using a single cutting face?

In "Small" Engineering firms, the weapon of choice for removing big lumps would have been a shaper and despite the headlong rush for us Muddlers to try to emulate the latest industrial operations in a shed, I've never seen a multi inserted shaper tool.

As far as production machinists? perhaps we should rename the web site "Model and Production Engineering"

Regards Ian.

Not sure where I said Gary was doing it wrong, I simply pointed out that it may be a false economy as you will be wearing the few inserts used faster so in the long term will probably not save any money. If you figure in the fact the machine is running longer using more electric, you need to heat and light the workshop for longer and if ordering in batches of two postage will add up it could be seen as even more of a false economy.

Gary also mentions noise, this is partly due to the fact the two inserts are unlikely to both be engaged in the cut which gives intermittent loading on the mills drive train which is probably more likely if there are gears in the head rather than belts but the quill splines will still know about it. With more inserts in the head the machine will run smoother as there is likely to always be at least one insert doing some work