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Advice needed - internalizing injection mold making


Jun 23, 2002
Vancouver BC Canada
Hi again INJ:
I just re-read your first post and have a couple more comments:
When you mused about setting up your own mold shop from scratch, you talked about needing both sinker EDM capability and CMM capability.
Here's my take:

For making eyeglass frame molds you need neither.
You're making parts where the primary criterion is cosmetic, so the process you choose needs to be capable of making excellent finishes on your mold cavity surfaces but if you miss your target dimensions by a few microns nobody's gonna die.
There are a few places where the precision truly matters in moldmaking, but not that many and not that extreme either.
Remember, injection molds were being successfully built way way before all the fancy modern tech...I built a lot of tools in the 1980's with nothing more than a Bridgeport manual turret mill, a surface grinder, a Deckel pantograph and a manual lathe, and my shop was better equipped than many in my area.

If you already have a Brother and it's being used in the toolroom, you should try it for milling a mold cavity...maybe it'll be perfectly adequate for your parts.
IMO there is no need to invoke nanometer level precision here...you will be able to judge whether your cavities are good for your purpose just by looking at some test shots...if it looks good to you and the lenses fit , it's as good as it needs to be.
Your primary goal is to get inserts off the machine that need no benchwork...no parting line spotting, no polishing, no die grinding.
For parting surface work you need to be within 25 microns if your molded plastic is forgiving and doesn't flash easily...you need to be up to ten times better if it does flash easily, but you must remember also that your mold will inevitably deteriorate, and if it's aluminum, it may do so more quickly than you wish, so killing yourself to get it perfect won't help you as much as you might think.

A 5 axis machine will be a Godsend for you...thankfully you already know how to run those.
Does your Brother have a 2 axis rotary that's big enough to swing a mold insert?
If it does, my advice above is sound...if it does not, I encourage you to spend whatever you can, to get the best you can afford...Kern, Hermle, DMG, Grob, Mikron are all reputable brands you may invest in with confidence.
You are doing so to capitalize on the ability to get superb finishes right off the machine and avoid all that benchwork and sinker EDM work.
The exquisite precision is a nice bonus.

So I encourage you not to turn this into an exercise it does not need to be.
You're building mold cavities for eyeglass frames, not implantable medical device parts by the millions.