Is anyone hard turning core pins for injection molds?

[texas385]

Is anyone hard turning core pins for injection molds? Specifically the details on the molding surfaces of the pins (multiple steps, tapers, fillets, chamfers, etc.) If so, what machines are you using and what kind of tolerances can you hold? With the advances in machines and tooling we are wondering if it is feasible yet. Currently we are using tool room grinders with motorized spin fixtures.

 

[RCS Machine]

Is anyone hard turning core pins for injection molds? With the advances in machines and tooling we are wondering if it is feasible yet. Currently we are using tool room grinders with motorized spin fixtures.

Are you referring to TH (thru hard) pins or the standard, soft, core pins? We mill the soft CP's (depending on their geometry) and spin or burn the TH's

 

[texas385]

Are you referring to TH (thru hard) pins or the standard, soft, core pins? We mill the soft CP's (depending on their geometry) and spin or burn the TH's

I am referring to the thru hard pins

 

[DavidScott]

I do it when needed. The ones I get from PCS are 50-55 Rc so not too hard.

 

[toolmaker96]

We turn CX & THX pins daily. Biggest problem that we run into is the that you can get chipping at the shoulders between the stock diameter & where you turning. We have learded to overcome this for the most part, but it takes some trial & error.

 

[EmGo]

Currently we are using tool room grinders with motorized spin fixtures.

Toolroom grinders and "motorized spin fixture" ? Ick. If you can scrounge any Landis - 1R or the older C and CH models - or equivalent Cincinnati regular grinder, should be much happier.

Grinder is good. Remember that

 

[texas385]

What CNC machines are you using to turn these hard pins? What kind of tolerances can you hold?

 

[5 axis Fidia guy]

We do all the time, some are purchased, some are spun from bar stock, H-13, 420SS and S-7

 

[implmex]

Hi texas385:
The short answer is: "it depends".
I know that sounds like a bullshit cop out, but it's not.

What it depends on is the complexity of the form on the end of the pin.
If no elaborate dressing is required, it's faster and simpler to spin grind it.
If it's some weirdass profile like a sucker pin or worse, it's easier to turn unless it needs some nutso form tool or super fragile full radius blade that has to be wire EDM cut first.
I have both an Optidress and a Diaform, so I can dress most forms but what a royal PITA for only one or two pins.
If there's more it starts to look a little less daunting and more worthwhile.
Sometimes you can crush dress your shape easily, but not often.

Finally hard turning a pin is not that difficult unless the aspect ratio is awful...they're not that hard, as David Scott points out.

This is one of the very few times I'm going to disagree with EmanuelGoldstein about what machines to use. (sorry Emanuel...will we still be friends do you think?)
I find normal cylindrical grinders to be a real PITA for this sort of work because they're so clumsy and run big expensive wheels that you really don't want to form dress the shit out of if you can avoid it..
The best I ever used was a Brown and Sharpe #13...nice because it can run small wheels that I can dress on another grinder and then just pop onto the B&S, still on the hub it was dressed on.
A shop I worked at had a setup like that...it's so long ago that I can't remember what the other grinder was but it was a B&S too (Micromaster maybe??) so the wheel hubs were interchangeable.
Worked like a hot damn, but it was still a pain to dress the wheels even with the Optidress and the profile projector that surface grinder had on it.

But many of the guys still just ran the pins with the spin fixture on the surface grinder...even with the B&S #13 in the shop.
If there was only a few pins to do, they couldn't be bothered to move the wheel to the other grinder and they really liked the profile projector on the machine.

A Cincinatti Monoset is another grinder I'd happily have in the shop for this kind of work...same reason I like the B&S #13.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[texas385]

Hi texas385:
The short answer is: "it depends".
I know that sounds like a bullshit cop out, but it's not.

What it depends on is the complexity of the form on the end of the pin.
If no elaborate dressing is required, it's faster and simpler to spin grind it.
If it's some weirdass profile like a sucker pin or worse, it's easier to turn unless it needs some nutso form tool or super fragile full radius blade that has to be wire EDM cut first.
I have both an Optidress and a Diaform, so I can dress most forms but what a royal PITA for only one or two pins.
If there's more it starts to look a little less daunting and more worthwhile.
Sometimes you can crush dress your shape easily, but not often.

Finally hard turning a pin is not that difficult unless the aspect ratio is awful...they're not that hard, as David Scott points out.

This is one of the very few times I'm going to disagree with EmanuelGoldstein about what machines to use. (sorry Emanuel...will we still be friends do you think?)
I find normal cylindrical grinders to be a real PITA for this sort of work because they're so clumsy and run big expensive wheels that you really don't want to form dress the shit out of if you can avoid it..
The best I ever used was a Brown and Sharpe #13...nice because it can run small wheels that I can dress on another grinder and then just pop onto the B&S, still on the hub it was dressed on.
A shop I worked at had a setup like that...it's so long ago that I can't remember what the other grinder was but it was a B&S too (Micromaster maybe??) so the wheel hubs were interchangeable.
Worked like a hot damn, but it was still a pain to dress the wheels even with the Optidress and the profile projector that surface grinder had on it.

But many of the guys still just ran the pins with the spin fixture on the surface grinder...even with the B&S #13 in the shop.
If there was only a few pins to do, they couldn't be bothered to move the wheel to the other grinder and they really liked the profile projector on the machine.

A Cincinatti Monoset is another grinder I'd happily have in the shop for this kind of work...same reason I like the B&S #13.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

What machine are you using for the hard turning?

 

[implmex]

Hi again texas385:
You wrote:
"What machine are you using for the hard turning?"
A vintage 2007 SNK Prodigy gang chucker.
Bog standard nothing special machine.
You really don't need anything outrageous to do this kind of work.
I paid $13,500.00 for my machine used off EBay in 2013.
It'll do hard turning just fine.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[EmGo]

I'm going to disagree with EmanuelGoldstein about what machines to use.

That's okay ... as long as you don't recommend hard turning

I just like the solidity of a regular grinder, and the 100 gallons a minute coolant and shielding, and the wheel you don't have to dress every twelve seconds.

It is kind of a bitch to swap out the wheels tho, so other people can have a different opinion ...

The best I ever used was a Brown and Sharpe #13...

Webster had one, we did finicky little stuff like grinding the radius on tops of bucket followers for his offlehowsers ... I don't think he ever finished a Indy race tho, so not sure how well they worked It's a nice grinder but I still like something sturdier.

 

[implmex]

Hi again Emanuel:
Yeah this is a place where our differences of opinion are probably pretty trivial.
I've ground pins and necked cutters on a Myford and I was able to do just fine.
But the B&S #13 was just so much handier for small stuff and for dressing little wheels with multiple angles or radii.

I remember now too, a Swiss T&C grinder whose name escapes me but was set up as a cylindrical grinder (Christen maybe??) that was part of the shop where I did my apprenticeship.
One of the things I was asked to do there was to design and build a pair of sprung steady rests that would allow us to cylindrical grind really skinny pins...like 1" long and 0.040" diameter.
What I came up with was the fingers coming in toward the workpiece at 120 degrees and 240 degrees with the fronts ground away almost to center, so the wheel could still clear them.
They would stabilize the part enough to allow grinding it and since they were set 120 degrees apart, they wouldn't deflect the part (very much) unless the spring pressure was set way too strong.
We eventually replaced the springs with adjustable weights on levers so we could control the pressure easily and that made a big difference.

Not relevant to the OP's question I realize...so my apologies, but the idea of hard turning pins at crazy aspect ratios without some kind of support IS relevant to the conversation.

The take home is that you can get away with some things by grinding that are much harder to do by turning.

I wonder if a Swiss could solve that problem...certainly having the tools snugged right up next to a guide bushing is appealing, but it really restricts how short a core pin you can actually turn, and I have no idea if it would be a practical alternative since I've never run a Swiss.

Maybe TeachMePlease or one of the other Swiss gurus on PM could chime in.

Cheers


Marcus
www.implant-mechanix.com
www.vancouverwireedm.com