# Machining Custom Mold Ejection Pins?



## Mike28303 (Jan 31, 2017)

Greetings,

I am trying to make an ejection system for my small aluminum molds with my Taig Mill, similar to what Mr. Socha does in this video (specifically the mold shown during 2:50 - 4:46):






While his mold and ejection pins are made out of brass, he mentions that perhaps brass is not an optimal material for the pins because the pin surface will gall easily. My subsequent thought was to use steel instead.

My initial plan was to buy O1 Precision Rod (from eBay), but I don't think I have the equipment to cut it to length accurately (I don't have a lathe). The tolerance of the length needs to be within .001”.

I thought about cutting the O1 rod close to length with a cutting wheel, then parting it off to length with the stock held in my mill's collet like in this image:




But I think cutting O1 might require rigidity that my mini mill does not have. Perhaps I'm mistaken?

My next and current plan is to use cold-rolled steel at 3/16” diameter and turn it down to 1/8” with HSS tools.

Do you think my plan is good? Maybe brass or aluminum ejection pins would suffice? If I need to go with steel I would prefer to use the O1 precision rod, but I don't have the means to cut it to length accurately.

Machine Details:
Taig CNC Mill with Ballscrews.
1/4 HP spindle motor
RPM Options: 1050, 1650, 2600, 4200, 6700, 10600

Any advice would be appreciated!

- Mike


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## willthedancer (Jan 31, 2017)

Ejector pins are available finished. We always cut them off with a hot saw and used a v block to dress the end on a disc sander. They are pretty hard. I think the pattern shop bought them from Stephenson Pattern Supply.


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## Wreck™Wreck (Jan 31, 2017)

Rough saw then place in mill vice and face the ends with an end mill to length, a lathe is faster but not required. If many parts are needed set a work stop and a table stop and have at it.

Or just buy ejector pins if available, McMaster sells them for example https://www.mcmaster.com/#ejector-pins/=165mevb


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## Mike28303 (Feb 1, 2017)

Thank you for the replies.



Wreck™Wreck said:


> place in mill vice and face the ends with an end mill



That is a great idea. I went ahead and tried it out on the O1 Tool Steel Annealed Rod, and the results were looking good - until the pin developed a burr around the edge of the face. I'm assuming this means my endmill is dull. It was likely my tinkering with the depth of cut and step-over that dulled the new endmill so quick.

I've listed my current settings below. Am I way off track? I was using HSS, but should I use carbide instead?

Taig Minimill
HSS 3/16" Endmill
Material - O1 Tool Steel Rod, Annealed Precision Ground
RPM - 1650
IPM - 3
DOC - .02"
Step-over - .01"


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## JimDawson (Feb 1, 2017)

looks like you could bump up the feed a bit.
Chip load = IPM / (RPM x F)
F = #of flutes

You normally want 0.001 to 0.002 minimum chip load.


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## Wreck™Wreck (Feb 1, 2017)

Everything but EDM creates a "burr", nature of the beast. Debur and carry on.


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## Mike28303 (Feb 1, 2017)

JimDawson said:


> looks like you could bump up the feed a bit.



Thank you! I went ahead and tried that but it did not appear to fix the large burr issue. Maybe on a more rigid machine it would work. I'm not comfortable with the noise the Taig makes as it takes these cuts into such hard material - before O1, the hardest thing I've cut on it was mild steel, but I almost entirely mill aluminum. Maybe I'm just not used to hearing it cut like this. 

I'm wondering if milling O1 tool steel is asking too much of a small machine. I'm about to check the backlash and tram of the machine after all this O1, just to see how it affected my recent tuning.



Wreck™Wreck said:


> Everything but EDM creates a "burr", nature of the beast. Debur and carry on.



Sorry, I should have described the burr more. It's not the regular burr I normally get when milling, it's much thicker - .005" thick, and at some points .004" wide (adding .008" to the pin diameter at the face). Maybe that's just how O1 burrs? If so, what would be the best method for deburring such hard steel?

If this O1 doesn't work out, I'll probably end up turning 3/16" cold-rolled steel down to 1/8" as mentioned at the start of this thread.


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## JimDawson (Feb 1, 2017)

Unhardened O1 machines pretty nice, one of the more forgiving tool steels to machine.  Maybe I missed that this was hardened O1  In that case, a carbide end mill would be my choice.  If it's hardened, any machine would be noisy.

For deburring, I would use a disk or belt sander, a bench grinder would work also to get most of it, then stone to finish.  Just takes a steady hand


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## Mike28303 (Feb 2, 2017)

JimDawson said:


> a carbide end mill would be my choice.



Thank you for the carbide suggestion and deburring advice. I just tried a carbide endmill this morning. MUCH better. I began with about a .0005" chip load, because I was paranoid, and had no clue what to expect. It made a pleasant milling noise, with a very tiny burr. I'm going to run a few more operations to make sure my endmill doesn't become dull after a few cuts like with the HSS. 

If it works well, then I think a solution has been found! I really wasn't looking forward to turning 3/16 down to 1/8 with a .0005 tolerence, while learning how to shape HSS and turning with my milling machine! 

Here is the description that was on the O1 listing: "O1 Tool Steel Round Rod, Polished Finish, Precision Ground, Annealed". I have no clue if that means hardened or not. If this stuff hardens with heat, then perhaps it hardened the tips when I cut it to length with a cutting disc (It turned the ends of the rod blue).

I plan on buying some more O1 stock from a seller that adds "ASTM A681" to the listing title - I did a quick search online, and it appears this is merely a standard for metal properties. My previous stock did not say this, so will buying the "ASTM A681" O1 have much of a difference in milling?

I used the following settings for the this morning's milling:

Taig Minimill
Carbide 1/8" Endmill
Material - O1 Tool Steel Rod, Annealed, Precision Ground
RPM - 6700
IPM - 10
DOC - .02"
Step-over - .01"


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## JimDawson (Feb 2, 2017)

Sounds like you have it nailed! 

Annealed = not hardened.


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