Milling procedure confirmation

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Mr Ron
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Re: Milling procedure confirmation

Post by Mr Ron » Sun May 05, 2019 1:38 pm

I believe there are inserts available for face mills that are HSS to replace carbide inserts.
Mr.Ron from South Mississippi

12L14
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Re: Milling procedure confirmation

Post by 12L14 » Sun May 05, 2019 2:58 pm

Yes and no, usually they are not " true" hss, but "only" so-called powder hss(some say they are much better than "real" thing).
Tool&die maker since yesterday ;)

pete
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Re: Milling procedure confirmation

Post by pete » Sun May 05, 2019 3:06 pm

Mild steel has a general starting point of just about 100 fpm with standard HSS RSG. Carbide "as a starting point" maybe 300 to possibly as high 500. Some types can go a great deal faster but these are ball park numbers That's what the books say. What's almost never mentioned is those numbers assume the reader is an industrial user with rigid machines and flood coolant. Intermittent use of cutting fluids is a bad idea with carbide due to the thermal shock problem. Without high volume flood coolant and cutting dry one trick I figured out is reading your chip colors. For our general equipment sizes, rigidity, tool design and carbide types you want at most for the chips to turn a light tan or brown as there coming off the material. After there cut off then turning blue a few seconds later is still fine. Getting that blue or purple color instantly in the cut means your too high and vastly reducing the cutting tools life. So I start under what the books say then work up to that tan/light brown color. Do it enough and you start to have a good idea of how low you can start with that particular tool and it's radius and material type. The chip color idea works equally well on a lathe. And I'd figure a tooth load of at least .002" - .004" minimum for feed.

If you can? I'd bandsaw most of that material off first. That's how it would be done in industry since it's faster and your not using up cutting edges turning all that waste into chips for no good reason. With everything else being equal drilling and sawing is alway's a faster bulk metal removal method than straight machining would be. Plus it's a whole lot cheaper. If you had an inch to remove off the end of a board would you make multiple passes with a router reducing it to size or use a circular saw, table saw and just cut that one inch off? In some industry's and using CNC it might make sense to not saw, but there profit ratio per part dictates what actual methods get used.

Harold_V
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Re: Milling procedure confirmation

Post by Harold_V » Sun May 05, 2019 4:03 pm

Determine chip load by multiplying the number of cutting teeth by the spindle speed. Multiply the sum by the desired chip load, and that will give you the feed rate in inches/minute. It's a good idea to not use less than a thou (prevent unnecessary rubbing) feed rate, and to not feed such that you overcome the rigidity/power of your particular machine. These things are best determined by performance, which you will observe as you increase feed, and even speed, of your cutter. As has been mentioned, pay close attention to the color of chips.

One more thing. Roughing generally demands greater feed rates than does finishing. If finish is important, I fully endorse the notion of using a fly cutter for finish cuts. With a fly cutter, you can increase spindle speed, lower feed rate, and get a wonderful finish, assuming you limit the depth of cut to no more than a couple thou per pass.

H
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pete
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Re: Milling procedure confirmation

Post by pete » Sun May 05, 2019 5:39 pm

Exactly what Harold said, I forgot to mention about taking an actual chip and not letting the tool rub. Fly cutting? YT is full of examples of purpose designed fly cutters taking some pretty aggressive depths of cut. Yes those tools are designed to do it. They even show some impressive finishes while doing so. The machine tools there being used on mostly wont. As Harold pointed out,fly cutters are a finishing tool only and certainly not a cheaper replacement for a face mill. That single intermittent tooth load hammers on the machines spindle bearings and splines. Yeah they'll do it for awhile with no apparent damage, that doesn't mean it isn't happening. That's why you use a face mill instead. You need at least two teeth in the cut during the whole revolution so that hammering doesn't happen. It still will at the start and end of the cut, but that can't be prevented. But for the most part the machine is then taking a gradual start to the chip formation over the majority of the surface. So reducing the depth to a light finish cut while using a fly cutter is much kinder to those expensive replacement parts. Tormach and Suburban Tools to name just two make heavy duty fly cutters, oddly they neglect to mention that using them like they show is a real bad idea. If you pay attention to some of those videos you can hear that hammering happening. I've got one that I think is no longer made, it uses the round carbide replacement tips. It leaves a great finish on almost anything with light cuts and is dirt cheap to operate since the tip can be slightly rotated if the current position becomes worn or chipped.

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BadDog
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Re: Milling procedure confirmation

Post by BadDog » Mon May 06, 2019 10:40 am

Chip load is a factor per insert. More inserts means more feed for same chip load. Chip load is also a factor of material and insert geometry, limited by horsepower and rigidity. Back when I started, I had some basic rule of thumb starting points, but on a typical manual mil, you don't have feeds in discreet distance/time values. So it's largely a moot point. I've gotten to a point where I can guess at the right feed and not be too far off, then fine tune as the cut progresses. Basically you are looking for solid well formed chips without the machine complaining too much. Even after getting it cutting good you'll sometimes need to tweak it further if you begin to encounter chatter, though speed is most useful there. I also tweak it (lower) during parts of interrupted cuts where there is too much banging due to inability to ramp the entry etc,

Edit: Oops - didn't realize this had rolled to page 2...
Russ
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RSG
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Re: Milling procedure confirmation

Post by RSG » Mon May 06, 2019 4:33 pm

More great advice, thanks guys....

Pete, good idea about band sawing it. I might ask my friend as his machine shop if I an borrow his if I have time. I've been neglecting getting this done so if his is busy I'll just have to use the mill.
Vision is not seeing things as they are, but as they will be.

rjitreeman0909
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Re: Milling procedure confirmation

Post by rjitreeman0909 » Fri Aug 02, 2019 9:46 am

If they are simple wedges, no step or shoulder, would an initial bandsaw or cutoff saw operation speed the metal removal and possibly result in two wedges from one raw block?

RSG
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Re: Milling procedure confirmation

Post by RSG » Fri Aug 02, 2019 5:07 pm

rjitreeman0909 wrote:
Fri Aug 02, 2019 9:46 am
If they are simple wedges, no step or shoulder, would an initial bandsaw or cutoff saw operation speed the metal removal and possibly result in two wedges from one raw block?
No doubt it would have but to be honest it didn't take more than 20 minutes to do each part as it was.
Vision is not seeing things as they are, but as they will be.

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