Material Selection: 6"X8"X1" die holder for 75T Ironworker
I'm going to machine a new die holding plate for my 75T Edwards Ironworker. The plate is 6" X 8" X 1" thick. It is backed up by a hardened plate so the die holder itself doesn't appear to need super strength. The dies about 2" in dimeter and the die hole is located near the long edge of the plate - with just 3/8" between the edge of the die hole and the long edge of the plate. I mention this because a 3/8 set screw holds the die in place so the metal needs to be tough enough to hold the threads for the set screw.
I don't know what the current plate is made out of so I'm hoping someone can suggest some material.
Right now I'm thinking about 4140, or maybe just 1018 or A36. There are some other tapped holes in the plate and the existing material is fairly tough - I was unable to clear out the threads with a cheap tap, but I've been told that the plate is not heat treated.
Any suggestions would be appreciated.
I bet 90% of the refits just have A36 in that location. If you wanted to get fancy a piece of Stressproof or 1144 for ease of machining would be more than adaquate. IMHO 4140 would be overkill.
What is the thread on the setscrew now. If it's coarse thread then the material is more likely mild steel. If you switch to a harder material then you might consider a fine thread series.
3/8" NF Thread Insert in A-36?
Thanks for the tip! I think I'll go with A-36. Your intuition about the thread on the 3/8 set screw is right - it's a course thread. This is one of my complaints with the original - the threads for the set screw are very loose.
One of the things I'm thinking about is using a thread insert on the new unit - maybe even go with a fine thread. If I understand things correctly, thread inserts are hardened steel and the combination of the fine thread and the hardened steel should make the design more reliable - i.e. tighter threads / longer life.
Any comments / suggestions? The idea came from an a person I used to know who worked for Heli-coil. He told me that some engine builders installed thread inserts to increase the strength of the overall engine setup. Was his just "advertising"?
you put too much pressure on them and they unwind and jamb up
keyed hardened thickwalled insert
Whippin is right on the money. Helicoils fail always at the worst possible time. They were never intended for frequent use.
Those keyed inserts are great but they're not a universal fix. You havbe to have enough wall to use them.
I would be amazed if Edwards used anything more than A36 in the originals- first, because it just isnt needed, and second, because Edwards sells on price, not expensive quality.
It is possible that a 75 ton Peddinghaus might have a better grade of steel- but they cost 3 times what the Edwards machines do.
The load on this part is simple downward force of the hydraulic ram- which 1" plate, supported as it is all around the actual hole, should be able to take. You arent putting 75 tons into trying to bend this plate- you are pushing UP TO 75 tons onto the punch, and unless something fails, that is where most of the force goes- into making the plate you are punching get a hole in it.
I suppose there is some possibility of the machined lip the bottom die sits on wearing over time- but I have never seen it happen on the ironworkers I have examined.
I am pretty sure my Geka ironworker only has the Basque equivalent of A36 in the die holders- it sure doesnt seem hard to me.
As for threads- these are not too critical. The only time you really use that set screw is when using a die that is directionally oriented- a square, an oval slot, or a keyway, for example. The set screw is meaningless for all round hole punching, which is 95% or more of most people's work. Even on the dies where it counts, I find that a combination of mill scale, lube, and tonnage pretty much cements the die in place after the first few holes- at least it seems that way to me, when I try to get em out again.
I think a standard 3/8" x 16 NC thread is perfectly adequate for holding in those lower dies, but if you really want to get fancy, go NC, and tap in 3/8x 24. You get full holding power with three threads, in most cases- so as long as your metal thickness is at least 1/8" thick, you should be just fine.
Progress Update: slow & typical!
Got the A36 - tried to clean up the edge with an endmill I had on hand - a 6-flute M-42 1-1/16 diameter (complete specs at the bottom of this post) running at <300 sfm. Took very light cut (0.010") running along the side and got a fairly poor cut - looks like tool chatter. So my first attempt at a machining setup wasn't all that successful.
Better, once I had the material all clamped up in the mill I realized that I really needed 1X6X10, not 1X6X8 like I had purchased! (Am I the only one who runs into these [self-created] problems?)
Given that the A36 is very tough, and I'm having trouble finding any Stressproof or 1144 in the dimensions I need, I'm thinking of going with 1018.
1) 1018 sound like a good choice? Again, this is a die holder for a 75T ironworker - it won't actually see a ton of stress, it just needs to hold the die in position - the force comes from the top.
2) Suggestions on endmills to:
(a) clean up the 1" sides where the stock has been cut from a larger 1" X 6" bar,
(b) chamfer one edge - the top 10" side has about a 1/4" chamfer,
(c) cut a 1/4" deep pocket 3" wide by 4" long to hold a hardened steel plate under the die - there are actually two 1X6X10 plates - the top one holds the die, the bottom one holds a hardened steep plate under the die
(d) cut the round hole for the die 2" or so in diameter using a rotary table.
My machine is a manual BP clone with power X-axis. 2HP motor.
I realize that I'll probably need multiple endmills for the job, but am really having trouble getting my arms around the proper tooling.
Finally, should I run the endmills dry or with coolant, or just cutting oil brushed over the top of the surface of the part between machining passes.
Endmill that produced a low-quality cut along the side of the A36:
Standard - Single End Mills Size: 1-1/16
Shank Diameter: 3/4
Length of Cut: 1-1/2
Overall Length: 3-7/8
Number of Flutes: 6
Material: Cobalt - M-42
Size (Inch): 1-1/16
Shank Diameter (Inch): 3/4
Length of Cut (Inch): 1-1/2
Overall Length (Inch): 3-7/8
Number of Flutes: 6
Rotation: Right Hand
Material Grade: M-42