Need advice on milling a 1-1/4" wide x 8" long slot into 1/2" mild steel plate.

[guythatbrews]

The YouTube warriors are getting poo pood here for the go to cut wheel but…

The Op could have that slug dropped out of that plate in less time than it took to write the first post.
Drill the corners with to 1/2”, leave the layout lines and finish on the mill/drill with just about any little end mill.
You will need to slice from both side and fuss at the ends to get enough cut that you can break the slug out.

The only problem is the off chance the op shatters the disk or otherwise let’s it go to crap with his fingers hands at risk from those effective but sorta dangerous wheels.

The guy has a mill drill. May not be the best to mill with but way better than cutting through 1/2" with an abrasive saw, and that's not even counting dealing with how do you handle the end geometry. What a mess!

Another way to tackle this on a mill drill is cut a slot around the periphery with a 1/4 2 or 3 flute end mill. Two passes down minimum maybe 3 or 4. Make the slot ends square. Leave a few places uncut to hold the slug. Hacksaw those places and let the slug fall free. Finish slot.

 

[Trboatworks]

The guy has a mill drill. May not be the best to mill with but way better than cutting through 1/2" with an abrasive saw, and that's not even counting dealing with how do you handle the end geometry. What a mess!

Another way to tackle this on a mill drill is cut a slot around the periphery with a 1/4 2 or 3 flute end mill. Two passes down minimum maybe 3 or 4. Make the slot ends square. Leave a few places uncut to hold the slug. Hacksaw those places and let the slug fall free. Finish slot.

Cut wheels work.
I cut lots of plate with them back in the dark ages.
Sure the ends will be a bit of a fuss and probably should just drill those but..
With a light mill I wouldn’t want to clean up a ton of chain drilled lines.
A good hand with a cut wheel and there is very little left to do on the long sides.
Yes on the mess- I always would take it outside to keep the grit out of the shop.

What’s this for anyway?
One of the online shops will have this done and on the doorstep with the blank cutout pretty damn clean for low money.
Clean/close enough?

 

[guythatbrews]

Cut wheels work.
I cut lots of plate with them back in the dark ages.
Sure the ends will be a bit of a fuss and probably should just drill those but..
With a light mill I wouldn’t want to clean up a ton of chain drilled lines.
A good hand with a cut wheel and there is very little left to do on the long sides

I agree and wouldn't want to chain drill this anyway. And I agree you can saw it out with an abrasive saw. It's just my last though if I have a milling machine. Even a light one.

 

[Trboatworks]

Yeah- I am so tired of clamping stuff to the porch and going at it with wheels I wouldn’t do it either.
It’s just the gearing up- dust mask, gloves glasses and ears.
I always came back in the shop cursing but…
It got er done lol.

 

[Ox]

I'd resommend that you just mill it out and forget the whole torch thing.
I'm not seeing how that is going to save any more on one side than it takes on the other, and at least you wouldn't have to deal with the HAZ.

But that would go a LOT better if you have an air hose available to keep the cut clear of chips.


----------------

Think Snow Eh!
Ox

 

[dgfoster]

I've never milled a plasma cut part. The difficulty a jagged, handcut plasma job and milling on a drilpress aside, how can the HAZ get hard in mild steel. Not enough carbon to do that, is there?

It is not carbon that causes brittle hardening of plasma cut parts. Nitrogen from the air nitrides the surface. Cutting that nitrided surface is miserable. It is possible to use cover gases for plasma cutting to prevent nitriding, but I don't think that is common in most shops. Getting under it and lifting it off can work if the edge is uniformly cut. But a hand cut edge? Not likely and given the minimal cut that a mill/drill can do, getting under the nitride would be practically impossible.

Denis

Added: I machined a bunch of laser cut parts a while back and they had no discernable edge hardening. Water jet also (of course) leaves a sweet soft edge.

 

[Bill D]

Drill a full width clearance hole at each end. Mill the sides parallel and go to town with your power hacksaw. Don't have a power hacksaw, use a sawsall.
Bill D

 

[memphisjed]

there is enough carbon to make cold chisels out of mild steel using soapy brine (super quench). Plasma gets the edge very hot, expanding and contracting it to limits. It is work hardened. Super quenched by thermal mass of parent stock, with the carbon from vaporized metal being sucked in as material is in expanded state, plus nitride, plus work hardened- the haz layer is over 1/32", I find just over a 1/16 in 3/4 stock to get to the nice soft stuff.
torch cutting gives the parent material heat, dispersing the temperature difference. much shallower haz.

 

[guythatbrews]

there is enough carbon to make cold chisels out of mild steel using soapy brine (super quench). Plasma gets the edge very hot, expanding and contracting it to limits. It is work hardened. Super quenched by thermal mass of parent stock, with the carbon from vaporized metal being sucked in as material is in expanded state, plus nitride, plus work hardened- the haz layer is over 1/32", I find just over a 1/16 in 3/4 stock to get to the nice soft stuff.
torch cutting gives the parent material heat, dispersing the temperature difference. much shallower haz.

The nitriding stuff from plasma cutting I understand. And using oxygen plasma gas avoids nitriding. This all makes sense.

It's been 40 years since I had a metallurgy class but I do recall hardening low carbon steel by heating and quenching is not what we were taught.

And I think work hardening requires plastic deformation performed below the transformation temperature. Don't think heating and quenching low carbon steel, or any steel, work hardens it.



I'm also suspect

 

[memphisjed]

The nitriding stuff from plasma cutting I understand. And using oxygen plasma gas avoids nitriding. This all makes sense.

It's been 40 years since I had a metallurgy class but I do recall hardening low carbon steel by heating and quenching is not what we were taught.

And I think work hardening requires plastic deformation performed below the transformation temperature. Don't think heating and quenching low carbon steel, or any steel, work hardens it.



I'm also suspect

The work hardening is after the quench while the material shrinks. If you slice near a plasma edge it will curl far more than milk or torch cut edge. The edge is poor steel worked and heated and moved beyond civilized. Plasmas are wonderful, not elegant method, I think the most brute force possible to shape metal. That includes shearing.

 

[metalmagpie]

I would not try a rotabroach in that milldrill. They don't like floppy setups but do cost money. Maybe you could get a hole saw to go that deep but rotabroach, risky.


Wait wait wait wait wait ... let's say this again, I didn't even think of this warning - do not ever ever ever ever hold an end mill in a drill chuck. That's a recipe for disaster.

Mill drills are Morse taper (some of them) but they have drawbars. So they can mill slots.
Rotabroaching on a mill is entirely possible. Just use a 3/4" collet and have at it. The cutting forces are much less than you'd think. Use lots of oil. You will have to manually clear the slug after each hole. A mag drill has a nifty arrangement that ejects the slugs when you raise the spindle.

metalmagpie

 

[Tony Quiring]

We once cut 1 inch steel plate with 1/2 inch end mill, was on a BP, but it worked...

Made a sled for log splitter, quite a few cuts.

If the op can fixture the plate well, lock the table in x while cutting y, and opposite when doing opposite, he could just mill out the center.

But, he needs a good 2 flute 1/2 or maybe 3/8 end mill.

Mist coolant so the air can clear the chips.

Go SLOW, for RPM, depth of cut and cutting speed.

Depth of cut no more than 0.050, maybe 0.025.

That is 10 20 20 passes per side, do one side at a time.

Continue all the way to the corners until last 1/16 inch of thickness , then stop short, this is to hold the slug until finished.

When through use a reciprocating saw to cut to the corners.

It will take a LONG time ad make a big mess.

 

[joe28704]

So nobody ever answered how can mild steel get harder or even tougher in the HAZ? Not enough carbon, right?

Well I just cut some plate with the plasma cutter and the "rind" will not take a file. Had to grind the skin off maybe ( guessing) 10 to 30 thou to get to where a file could cut it.

 

[joe28704]

Cut wheels work.
I cut lots of plate with them back in the dark ages.
Sure the ends will be a bit of a fuss and probably should just drill those but..
With a light mill I wouldn’t want to clean up a ton of chain drilled lines.
A good hand with a cut wheel and there is very little left to do on the long sides.
Yes on the mess- I always would take it outside to keep the grit out of the shop.

What’s this for anyway?
One of the online shops will have this done and on the doorstep with the blank cutout pretty damn clean for low money.
Clean/close enough?

Two pieces necessary for tilt front end mechanism for 57 Chevy. I'll consider cut wheel, I'm leaning towards plasma cut most out leaving 1/8" use grinder to remove 1/16" of the Heat Affected Zone then mill the remaining 1/16 long flats so cam follower can roll inside w/o roughness.
Never thought about having online shops do it. Plates are big though. I hate to cut wheel two feet of 1/2" plate by hand.
Thanks for the idea.

 

[joe28704]

Mill drills are Morse taper (some of them) but they have drawbars. So they can mill slots.
Rotabroaching on a mill is entirely possible. Just use a 3/4" collet and have at it. The cutting forces are much less than you'd think. Use lots of oil. You will have to manually clear the slug after each hole. A mag drill has a nifty arrangement that ejects the slugs when you raise the spindle.

metalmagpie

Yes this mill drill has

That was my thought and hope about the carbon. Hand cut yes hopefully not too jagged as it will be with a template to guide it.

Just tested that plasma rind with a file , its hard as hell. Layer is only (guessing 10 to 30 thou deep then its millable again.
So one method is plasma then grind then mill.

 

[dgfoster]

Well I just cut some plate with the plasma cutter and the "rind" will not take a file. Had to grind the skin off maybe ( guessing) 10 to 30 thou to get to where a file could cut it.

That is the nitride layer. Reading up the thread it looks like there are skeptics of the nitriding affect of air/plasma. To speak to that skepticism here is a quote from Hypertherm ( you’d think they might know something about it) : “Some nitriding and oxidation of the cut surface occurs with air plasma”

Here is the reference:Hypertherm on Nitriding.
Denis

 

[joe28704]

Mill drills are Morse taper (some of them) but they have drawbars. So they can mill slots.
Rotabroaching on a mill is entirely possible. Just use a 3/4" collet and have at it. The cutting forces are much less than you'd think. Use lots of oil. You will have to manually clear the slug after each hole. A mag drill has a nifty arrangement that ejects the slugs when you raise the spindle.

metalmagpie

Yes this mill drill has a R8 collet chuck so it "can" mill. 1-1/4 "Annular cutter with 3/4" weldon shank should fit the 3/4" collet then chain drill as you said.. It's this method or Plasma cut to within 1/8 of mark then hand grind 1/16 of that down to remove the HAZ hard stuff then finish milling last 1/16 to mark. I think I'm leaning toward annular cutter as the hand drawn plasma cut will be is not as predictable/repeatable.

 

[joe28704]

Yes this mill drill has a R8 collet chuck so it "can" mill. 1-1/4 "Annular cutter with 3/4" weldon shank should fit the 3/4" collet then chain drill as you said.. It's this method or Plasma cut to within 1/8 of mark then hand grind 1/16 of that down to remove the HAZ hard stuff then finish milling last 1/16 to mark. I think I'm leaning toward annular cutter as the hand drawn plasma cut will be is not as predictable/repeatable. It's a toss up , I got to order 1-1/4 annular cutter but got everything to do the plasma route.

 

[memphisjed]

McMaster and others sell an annular cutter adaptor. It has a 3/4 shank and a spring chamber to hold standard ejector pins. Without it the slugs can really stick in the cutter, with it- they self eject.

 

[joe28704]

Well, machining guy! Welcome to the club! Learn about sfm, surface feet per minute. It's the peripheral velocity of the od of a spinning cutter in a mill or workpiece in a lathe. You can find charts for the recommended sfm for material and operation. Peripheral cutting velocity is one on the fundamental building blocks on your machining journey. How fast you turn something isn't magic or guesswork. It's practical science peppered with experience.

Since this doesn't look like a production job use 200 sfm for carbide or 75 sfm for HSS. The numbers in the charts aren't ever hard and fast, just starting points.

The formula is rpm=sfm*3.82/dia so for a 1/2" cutter at 75 sfm the rpm is 573. A bit faster or slower is fine.

You threw us all with your first pic, which looked like simply a drill press with a drill chuck. As you said it's a mill drill, and it has an R8 spindle. The BEST way for you to hold the cutter is an R8 collet. Second best is the collet chuck in your last pic, second best since it has a lot more overhang. Overhang is your enemy.

You'll be fine. Remember it's very important to lock the axis that is not in motion when you mill. Probably never climb mill on your mill drill unless its a dead pass or very light cut. Else the workpiece will self-feed very rapidly the distance of the backlash.

Thank you very much. I actually understood that. Thanks for the tips , not any more than I need and not any less!
I think I'm headed toward plasma cut to within 1/8" of line, hand grind HAZ down 1/16", mill final 1/16 per your advice.