Milling a small slot, how??

A

alinwa

oft dis'd member
I recently milled a short slot through a cast trigger guard for the Jewell trigger to clear. The action is FAT, the trigger is on a hanger and the stock is too shallow.....and I didn't want to shorten the trigger.


Anyway, The slot is about 3/16 wide, I milled it using an endmill slotting progressively deeper and it came out looking like dung. I filed it to clean it up.

My question is, what would be the appropriate cutter to just plunge thru and then walk sideways?

Will a rougher work? Do they come that small? Is there a "sheet cutter?"

I'm a rank newbie on the Bridgeport :)

Thanks
al
 
Use a nice sharp two or four flute center cut end mill and because of the small diameter make sure you run it fast enough. Once you make your slot skin a little bit off each side by "climb milling". In other words run your cutter with your work rather than against it. This should give you a nice finish.
 
al
I have done exactly what your asking. I also had the same result until i kicked the speed way up. Lee
 
look up s.f.m surface feet per minute all materials use a specific range it will make your life a whole bunch simpler, should be used on all cutters mills ,drills and lathe george
 
I will try the backwards "climb" cut and the higher speed :)

Now, that said, is it recommended that one cut a slot using the smooth flutes of a standard endmill? I've not had good luck milling slots via the "plunge through and cut sideways" method. Aluminum yes but steel, not so much. I have reason to slot a bunch of 1/4" plate for some brackets.
 
geo.ulrich said:
look up s.f.m surface feet per minute all materials use a specific range it will make your life a whole bunch simpler, should be used on all cutters mills ,drills and lathe george
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Thanks George. I think I'll print off and laminate a sheet and hang it with my drill/tap index chart. Two things I consult a lot with greasy fingers :)

al.
 
Think carbide but remember to keep cutting speeds correct

A carbide end mill might help as they are more rigid but make sure your setup is tight. ie gibs snugged up a little drag induced so there is no way for anything to grab or jump when the cutter is working.
 
I'd suggest using a carbide 1/8" end mill plunging down through the trigger guard and making your slot in the middle. Then open up the slot with the sides of the end mill on each side of the slot. Finish the cuts by climb milling for a smoother cut. I'm not sure what speed I run my end mills as my mill has a VFD on it. I run most end mills pretty fast though with either the second or third belt position on the high speed side of the belt drive mill, usually at 60Hz on the VFD which is normal motor speed.
 
Mike Bryant said:
I'd suggest using a carbide 1/8" end mill plunging down through the trigger guard and making your slot in the middle. Then open up the slot with the sides of the end mill on each side of the slot. Finish the cuts by climb milling for a smoother cut. I'm not sure what speed I run my end mills as my mill has a VFD on it. I run most end mills pretty fast though with either the second or third belt position on the high speed side of the belt drive mill, usually at 60Hz on the VFD which is normal motor speed.
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In most Aluminum alloys, and what we normally see are all alloys, you would run a HSS cutter at somewhere around 500-750 SFM, carbide about 2500 SFM.

That's about 18,000 RPM for the HSS and over 86,000 RPM for carbide for Mikes 1/8" endmill. Looks like you guys might be a bit slow!!
 
JerrySharrett said:
In most Aluminum alloys, and what we normally see are all alloys, you would run a HSS cutter at somewhere around 500-750 SFM, carbide about 2500 SFM.

That's about 18,000 RPM for the HSS and over 86,000 RPM for carbide for Mikes 1/8" endmill. Looks like you guys might be a bit slow!!
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Jerry, don't think I can run that fast at least with carbide. I might be able to get the 18000, but would have to look to see what the top speed is on my mill.
 
Mike Bryant said:
Jerry, don't think I can run that fast at least with carbide. I might be able to get the 18000, but would have to look to see what the top speed is on my mill.
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Mike, these are the theoretical speeds that SHOULD be run to effectively perform this machining operation (small slot in aluminum). With your Bridgeport type you will not get anywhere near the desired HSS speed let alone the carbide speeds. Mazak and some other top quality builders make machines with spindle speeds that go upwards of 40,000 RPM but just the bearing pack for some of them are in the $25,000-$40,000 range.

The best results in this application is to run the spindle at max rpm and hope for a good outcome.
 
Running a tool at a published SFM or calculated RPM has absolutely nothing to do with that tools cutting effectiveness. Every tool/material combination has a temperature threshold that results in tool breakdown or material gauling. The published data for SFM of a particular tool and material should be considered a maximum. Any RPM less than that maximum will create less heat all the way down to the tool not spinning or cutting anything, at which point, will last forever.

The calculation for a 1/16" endmill spun at 2500 SFM comes out to 154,000 RPMs! I could cut aluminum just as effectively, though slower, with that tool at 100 RPMs and it would likely last for years at that speed. A formula to write down or memorize is RPM=SFM/cutter diameter X 3.82. I highly suggest any machinist on any level owns a copy of the Machinisht Handbook.

What you are experiencing on a Bridgeport with changes in RPM, (as far as higher cutting speed being better), is changing the harmonic frequency of your setup. If you had no RPM limits, you would see the tool seem to cut better and worse at different RPMs. If you have a good rigid setup, you likely will see no effect in a change of RPM. The number one biggest error I see even very experienced machinists make is lack of rigidity in their setup. Typically the tool is sticking out too far. I train people to use the 3X diameter rule of thumb. If you have a 1/2" endmill, it should not be sticking out of your collet more than 1-1/2". A 3/16" endmill shouldn't be out further than 9/16". A 1" diameter part shouldn't extend more than 3" from your lathe chuck. Acceptable maching can be accomplished with less rididity than this rule but almost certainly compromises will have to be made. Ususally a reduction in RPM to overcome chatter.
 
Joe Woosman said:
Running a tool at a published SFM or calculated RPM has absolutely nothing to do with that tools cutting effectiveness. Every tool/material combination has a temperature threshold that results in tool breakdown or material gauling. .
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I see you have never done any high speed profile milling, like wing spars and such.

With what you just wrote I kind-of wonder if you have done much real machining at all.
 
JerrySharrett said:
I see you have never done any high speed profile milling, like wing spars and such.

With what you just wrote I kind-of wonder if you have done much real machining at all.
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Oh now that's funny! What does high speed profile milling, wing spars and expensive Mazak spindles have to do with the technical aspects of machining? Do you have anything technical to offer? There's no question you've probably seen a lot of machining. Now tell us how and why.

It would be absurd for me to go on about my qualifications. I'll just say I am an accomplished machinist at the very cutting edge of technology. If I need a qualifyer to back a statement I will gladly provide one.
 
Joe Woosman said:
Oh now that's funny! What does high speed profile milling, wing spars and expensive Mazak spindles have to do with the technical aspects of machining? Do you have anything technical to offer?

.I am an accomplished machinist at the very cutting edge of technology.
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Oh, Gosh, Gollleee, and I thought machining speeds and feeds was technical stuff??? How about M08 and M07??

Tell us about your accomplishments.... I'll show you mine if you will show me yours!!
 
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I looked at the top speed on my mill and it was 2670 rpm. With the VFD, it will probably do a little more than that. Top speed on my Kent lathe is 3000 rpm and that's scary when you put a barrel between centers and turn the lathe on and it gets up to 3000 rpm real quick. The Kent lathe has a high and low gear that will run up to 500 rpm on low and then will go up to 3000 rpm on the high side. It's pretty easy to be using the low speed side and have it turned up to 500 rpm. Turn the machine off. Come back, switch to the high side and get the 3000 rpm. It doesn't take long to turn the VFD knob down.
 
JerrySharrett said:
Oh, Gosh, Gollleee, and I thought machining speeds and feeds was technical stuff??? How about M08 and M07??

Tell us about your accomplishments.... I'll show you mine if you will show me yours!!
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No, speeds and feeds are not technical stuff. Neither is knowing what an M-code coolant command is. The proper application of such things IS technical stuff. This is the difference between the "machine operator" machinists and the guys that actually engineer machining operations.

I have been machining for 25 years. This I consider to be quite irrelevant. Many people spend a lifetime practicing mediocrity and accomplish little. Knowledge and proper application of it is what makes the difference. I started at the bottom and went straight to the top rather quickly. Blazing fast in fact. By the time I was 23 I was the shop foreman and technical leader of about 50 people. At this point I had moved to the top of three different companies, only moving on due to lack of growth potential. Self employment was the next avenue.

At 23 I started my first business with about 200K in equipment. (All financed. No silver spoons here). I gravitated to work that I had little competition with. This would be highly technical, difficult jobs that others couldn't do. 17 years later I own the company I first worked for. Most of my work is in the aerospace and defense arena with components that either sustain life, or take it.

I own five horizontal CNCs with pallet changers and full 4-axis motion. I have three horizontals with full 5-axis controls. Five vertical CNC mills, four CNC turning centers, optical and touch probe CNC CMMs, three seats of Mastercam CADCAM systems. I not only own the equipment but I have intimate knowledge of each of it. I work with designers and engineers on a daily basis. I work with tooling application engineers so I may understand the technology and apply it properly. I work with cutter grinders to improve on cutter geometry, creating better surface finish, tool life, etc. I design toolpaths to most effectively utilize the equipment and tooling.

I don't chose to buy a $600 endmill when you could buy the same size tool for $100 for no reason. I'm currently working on a job that the material alone costs over 10K each! You don't just crank up the RPM and "hope for a good outcome". You must know what is going to happen before it happens. Controlling every aspect of the operations.

If I ever state something about the tuning of a BR rifle I recommend people take it with a big grain of salt. I might just be talking over my head. If I'm talking about machining, it might be worth paying attention. Not sure if this meets your definition of "real machining" but there's a small peak at mine. Your turn Jerry.
 
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