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Hi,
I am wondering what is the proper way to drill holes for ejector pins. Textbook calls for +.002" to depth of 3x diameter and then + 1/32" all the way.
I am using 3/16" ejector pins. Do I drill a smaller diameter hole, then ream, flip the mold over and then drill to +1/32" oversize?
It's a class project and just drilling with a 3/16 drill seems to work, but I am wondering what is the proper way to do it?
thanks,
john
Text book is the way I was taught.Drill,ream,flip and relieve.
thanks,
I will give that a try. . . though it's tempting to just go with the 3/16 drill . . .
john
Remember drilling is essentially a roughing operation. You need a good hole for ejection pins. Drilling alone is not a good option. The extra relief behind the pins are so it does not bind or drag for ejection. Allows the ejection plate to 'slide' rather than stick with higher forces.
JohnJW
The text book is not quite right
You have to drill & ream or bore the ejector pin holes, the .002 clearance in most case's would not work, It depends on what plastic you are going to run in the mold, as to what clearance the ejector pins can have, most are .005/.001 clearance
You have to check the material spec to see what size Vents they recommend, then you will no from that, how much clearance you can have for the ejector pins
The clearance around the ejector pin is use as a vent
To much clearance & the injected plastic will flash down around the ejector pins
The drill relief in the back of the mold, does not have to be very big, next drill size is more than enough, it's only to give a easier path for the air in the mold to get out quickly 3X dia is ok for that pin size relief, but 3x dia would not be any good for .060 pin
A word of caution, many small ej pins are stepped, for example a .032 dia pin would have a .125 shank. So the relief for the pin would actually be around
.156 dia. Not just the next drill size over .032 dia.
5axisguy
That is correct, but in most cases with a .032 pin (anything smaller than .187) you want as small a relief as posible, Only open the large step size were it needs to be done, like in the support plate Etc
If you releave to much behind a small dia pin, when the part is ejected the pin's bow out into the big clearance , & in a short time they start breaking, have you ever wondered why the small pins break after a short time of use, This is one of the reason's to much pin clearance relief
for small pin holes, we generally use 1.0 or 1.5mm we just pilot dia 1.0mm all way thro and then wire cut the holes. since doing this 90% of all pin breakages resolved. and i've not had a pin seize up yet. also the pins or the holes do not wear either.
I like to drill from the front,then flip relieve and ream from the back.That way you won't get bellmouthed holes in the cavity area.
John Stearns
Hello John:
I agree 100% with John (brewzz). Ream from the back so you don't bellmouth the hole otherwise you'll get plastic flashing around the ejector pin.
I was taught to do it this way by my father 40 years ago.
First create a small hole with a drill spotface counter sink to ensure an accurate location and guide the drill, drill undersize through, flip, drill the clearance hole, then ream through and chamfer the clearance hole diameter in the back. If you don't use a drill spotface counter sink first the drill will wobble until it gets started and your location won't be accurate.
You'll also get a cleaner hole at the face if you control the speed of the reamer as it exits the steel or aluminum. If you let it pull and lurch through quickly or the hole won't be as clean. A little practice and you'll be a pro!
Have a terrific weekend!
Robert
3D Accuracy
Here is what I have found works when drill and reaming EJ Holes. using High speed tools.
1) drill size to be 3% smaller than reamer. ie: 1" Ø x 3% = .030 Ø smaller // 1/16 Ø x 3% = .002" smaller. using drill that is close to Ø
2) spot drill to minimum ream Ø ( if using manual mill, never move table. finish drill ream each hole)
3) only use new drills.
4) ream using only coolant. ream at same SFM as drill Ø , but twice the feed rate.
when reaming difficult materials. a test on scrap is always done
we went from the manual world to the cnc world. sometimes it takes a little longer to do a good job.
Gord