Building a bed turret

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RSG
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Re: Building a bed turret

Post by RSG »

I started the face milling today. Boy, this stuff is messy! black stuff everywhere.

I have a new question - I didn't realise i made these casting so thick! It's going to take forever getting them to the correct size using the facing mill. Is there a faster way to rough them out?

Image

Currently I'm running a 2" dia facing mill at 200 RPM, SFPM is slow, I didn't work out the speed though.
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pete
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Re: Building a bed turret

Post by pete »

That's roughly 100' per min RSG. You could probably step the rpms up to about 600 and that would allow triple your feed rate over what your now using. More speed = more dust and a wider area the chips are going to spread to though. The chips look good so your not feeding too slow. Good idea with your card board and vapor barrier plastic though. How's the new vise working?
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Harold_V
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Re: Building a bed turret

Post by Harold_V »

I have a distinct dislike for the dust that comes from machining gray or ductile iron. For that reason I use a shop vac to capture the discharge from the cut. Mine discharges outside, so the dust is removed from the building. You might consider that to help control the mess that comes from machining those metals. Your shop will end up a lot cleaner, in general.

Unless chilled (yours does not appear to be) you can take some serious cuts in these alloys. They are free machining. You're most likely to be limited by the horse power of the machine than anything else. With more than one tooth in the cut at all times, you may be able to take a much deeper pass. Keeping at least one tooth in the cut prevents spindle hammering.

H
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RSG
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Re: Building a bed turret

Post by RSG »

Thanks guys, I'll try increasing the RPM tomorrow. I have these inserts to work with also. Are either of these suitable? Pete, I'm happy with the barrier so far. It seems to be keeping things controlled inside the table. I wear blue nitrlie gloves while doing this and they are black now! Harold, So far the dust has been controled but maybe if I speed things up it might not.


Image

Another silly question, how do I tell what the SFPM is with my power feed? There's no real indication on it other than a dial from o - 10. Is it a simple case of timing it over a distance of say 6" and extrapolating?
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pete
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Re: Building a bed turret

Post by pete »

My power feed has the same stupid dial that doesn't tell you much. But chip size, surface finish and listening to the machine is to me a better indicator of feed rate. You can time it but it has to be done under the same depth and width of cut your taking and the spindle rpm you've decided on. Air cutting and trying to time that will give a much different feed rate than when the tool is under cutting loads. Maybe start a little too slow and keep adjusting the power feed upwards until the machine seems ok and your getting decent chips. My dro has a feed rate display, but it only gives you the distance traveled per minute. So even with that you still have to calculate how much each tooth is taking. And since your roughing I'd probably try that right hand insert. It's bigger corner radius should give better life. The left insert shape might? give you a better surface finish with a light cut for final size.
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Harold_V
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Re: Building a bed turret

Post by Harold_V »

Feed rate is a function of observation and understanding when one operates a machine such as yours (and mine). Experience dictates that you can increase the feed and/or spindle speed, assisted by the behavior of the resulting chips. This is best learned by experimentation, as there are too many variables for anyone to suggest what might be acceptable. Start slow and increase feed and speed until the machine behaves well and metal is being removed at an acceptable rate. Listen to the cut and the machine. If it sounds like it's struggling, could be you need to back off a little.

Do remember, when you increase spindle speed, in effect, you decrease feed rate (the amount per tooth diminishes), so do adjust them in conjunction with one another.

It's not good practice to allow a cutter to dwell. Keep the teeth loaded, which will prolong the useable lifespan of the inserts.

H
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RSG
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Re: Building a bed turret

Post by RSG »

Thanks Pete and Harold!

While I admit I lack experience milling anything more than aluminium I have done a couple dozen projects over the years in steel and have found that going slow with lower RPM always made the machine sound laboured. However, cranking up the RPMs and feed rate made it sound smoother. I can't say I've noticed differences in chip form but at least to my ear it sounds smoother less laboured if you will.

Thanks for taking the time to offer advice. I will try it today and reply.
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RSG
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Re: Building a bed turret

Post by RSG »

Well that's a whole lot better! Note the chatter but it only happens in some sections.

.05" doc, 800rpm. Happy with the results, a lot quicker....Thanks for the help!

Image




And thanks Harold for the warning on the chips, this stuff make my fingers and anything it touches black! Glad I made a shroud to contain most of it.
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pete
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Re: Building a bed turret

Post by pete »

Looks good. But that might not be chatter, my guess is possibly the odd chip getting dragged back into and under an insert. Chip recutting is always a royal pita, compressed air would make an even bigger mess, but maybe try a little higher rpm on the finish cuts to throw the chips off the part or a vacuum to remove them as fast as there being generated. But if it is chatter? A bit lower rpm and/or upping the feed a bit more should cure it.
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Harold_V
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Re: Building a bed turret

Post by Harold_V »

I'm not clear on what you describe as chatter. I see none.
Take note that the pattern I observe is normal. What I see is a cross hatch pattern, and that's a sign that the head of the mill is properly aligned with the table. You can expect a somewhat less than perfect surface due to the small amount of chip welding that occurs with cutting tools, even in cast iron. The deposit comes and goes, altering the depth of the cut in a minor way. Perfectly normal. If you slowed WAY down, it may even just go away.

You likely already understand that the black stuff is graphite, which is a reasonably good lubricant. That's what makes gray iron gray iron, and what makes it so friendly to machine. The alloy can hold only a given amount in solution, so the balance precipitates as graphite flakes upon solidification. In ductile iron, the same graphite precipitates as nodules, or spheres, which is the chief difference between gray and ductile iron.

H
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RSG
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Re: Building a bed turret

Post by RSG »

Pete, I did just that, adjust the feed/rpms accordingly but it would still do it to some degree in the same spots every time.

Harold, that squealing sounds is what I was mistaking for chatter but reading your reply has me thinking otherwise. Either way uping the RPM and feed rate has made it smoother and a heck of a lot quicker.

I use an app put out by "The Little Machine Shop" for feeds and speeds and while it seems to me (because I don't know any better) good, every time I run it by guys here or my machinist friend they always say the same thing, that it's too low! Is they a better app for figuring out cutter speed for various alloys out there?
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pete
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Re: Building a bed turret

Post by pete »

Harold might have nailed it with that chip welding. Have you got any large diameter fly cutters RSG? I have one that uses round inserts and it's my favorite tool for LIGHT finishing cuts. Less than .010" in steel and most times closer to 005". How true it is I dunno, I've read multiple times that today's industrial feed / speed recommendations are listed with the assumption flood coolant is being used so there too high when cutting dry. But it's probably safe to assume those cast iron speeds are calculated without coolant. Machinery's Handbook would be my first stop. My choice is I drop what they have to say by 20%-25% and work up from there and see how the machine and tool performs. DOC is more specific to the radius size on the insert. To me there's far too many variables involved to have any exact formula you can go by. So I use any chart as a maximum ball park number. Chip size, color, surface finish and listening to the machine seems to work better for me. If I had to guess, that LMS chart is meant for the sizes of machines they sell, so smaller that our baby Bridgeport clones. My X2 sized mill sure didn't like and definitely couldn't do what my clone does without a problem.
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