Should you run carbide with your machine at flat chat? Not necessarily.

If you're like me and use carbide tooling a fair bit, you may have read that it likes to run fast. This idea is further supported by the surface speed and feed recommendations you will often find printed on the back of those packets the inserts are sold in; and you might well have seen videos of those state-of-the-art industrial CNC machines in action getting perfect finishes every time.

So in an attempt to approach these ideals, you may be tempted to run your lathe or mill as fast as she'll go whenever you're using a carbide tool; and I myself have applied this mindset countless times. Lately though, I have had to temper this with caution. I do some volunteer work repairing and maintaining the trains at the Victorian Goldfields Railway which runs between the towns of Maldon and Castlemaine, and I would go flat chat when using the lathe there provided the work was not too big or unbalanced; which has gotten on the nerves of the other people there, including the workshop manager.

Many of these other people, including the works manager, are skilled machinists with decades of industry experience, and they tell me to also consider the stress that high speeds put on the machine you're using, particularly if said machine is old and a bit clapped out.

I thought I should share this lesson in basic workshop practise here as a word of caution to those of you who are just starting out in this whole game, and to see if any of our more experienced members have anything to say on the matter, and can maybe add something to this, as this has been a bit of a wake-up call for me, as I am admittedly rather stubborn in many cases.

I seem to be lucky in that I have developed a feel for the speed at which cutting is working well, but I use the same general types of cutters with the same relatively common materials I use for my own hobby use. If anything new, unusual, or exotic comes up, then I consult the reference information I can find and take that under consideration. I use indexable carbide, brazed carbide, and HSS tooling; depending on the task at hand.

I find that on my small machine I can't really get the speed up on carbide, but sometimes slowing down will work better than trying to go faster.

Watching some of the folks on Youtube seems to bear this out, as they seem to adjust speeds up or down based on how it is working rather than as fast as possible.

I also notice the Youtube people take into account the machine being used, as some of the big heavy machines can run with heavier loads than some of us can ever imagine.

--ShopShoe

Carbide tips are intended for use in high speed production and work well at high speeds
It does not mean that we model engineers with smaller lathes have to run the lathe at high speed
with big cuts.With a light rub with a diamond wheel to achieve a slightly sharper cutting
edge carbide tips can produce a good finish at slower speeds.As shopshoe as have not consulted cutting speed charts for a long time especially with the variable speed lathes which can be
adjusted while your machining

If you are in a production shop, time is related to money and the faster you can produce the parts, the more profit there can be. With that in mind, pushing the lathe to the max that produced acceptable parts is desired. In the past, that speed was limited by the use of the steel cutter that would get too hot if pushed too hard and lose its hardness. Carbides can retain the hardness with higher temperatures so they can be pushed harder, making for more profit. Eventually even carbide cutters dull so some smart person invented inserts that could be quickly replaced, returning the tool to production faster. That is where we are now in the evolution of tooling. To avoid the chipping of the sharp edge with the carbide they are not as sharp as they could be. If you are not into high speed production, sharpening the edge will make it cut better and take less power to do so.

flat chat? <--- not familiar with that one.

As for your machinist friends complaining about stress on a machine, it is hard to say if the complaint is valid at all. Just because you have a machine running at max RPM with a good feed rate doesn't mean the machine is overloaded in any way. That would depend upon the specifics of the machine and how much of an actual removal rate you are attempting.

So frankly I'd likely be arguing with the chap that is complaining because you are otherwise wasting time if you are using a material removal rate that is lower than the machine can handle. Frankly if you are working on train or locomotive related hardware you don't want to be wasting time if you expect to get the work done anytime soon. Being a volunteer shouldn't mean wasting your time that you offered up to the organization.

On the flip side there is little reason to achieve high removal rates in a home shop. Also most machines in a home shop can't handle such loads. So in my mind there is a huge difference here between home shop equipment and anything suitable for railroad maintenance.

Maybe I'm a bit oldschool but I would tend to agree with your colleagues at the repair shop. Just because a lathe was designed to run at high speed, high feed and deep cut doesn't mean it was designed to do all three at the same time. Old machines were designed around the tooling available at that time. So an 'old clapped out machine' may not be suitable for modern tooling methods. I imagine the volounteers can't afford to replace the lathe and spares might be obselete, hence their concerns. After all I hope you wouldn't drive a vintage car flat out down the motorway for 200 miles.

Good day,
I use replaceable 11mm inserts with a H&F AL51g machine. Depending on the diameter of the work piece I run at 350 or 500 rpm. Very infrequently a higher RPM may be required.
With a light cut rate on the last run the finish is mirror smooth.
I am unable to use flood cooling or lube in the area in which I work, thus the tips.
It all works remarkably well.
Regards to all,
Dennis