Mold maker blowing smoke at me?

Was a very useful discussion for me too, learned at lot about things I didn't know I needed to know!

Thanks

John Layne

I finally got to see the "RING". So I take it you have to have that little step? If you could blend that into one slope it seems like that would solve the problem.

BTW, to get in take the URL, remove the reference to the jpeg and then you can browse for that and everything else you have in that directory.

OH, IS THAT RIGHT? S___, that's not cool!! I'll have to fix that. Yes, I know that the step isn't right. I'm fixing it, but it ain't easy. Got one side fixed -- took a Surface Cut that itself took 25 surfacing steps to get to. And that's only one of the two sides I need to fix (opposite side -- 180 degrees). Doubtless I'm doing it very inefficiently, but I have my doubts it would be a whole lot faster at best.

John & others, on the "lock up" issue.

In all my time, which is now over 30 years, I've not had a pair of tapered cores that mate metal-to-metal lock up, though indeed I've not had a lot of them. The shutoff faces I have had have also tended to be relatively short,

Well, anyway, the parts as fixed can be seen at:

The two surfaces could not be blended, simply because they are from opposite sides of the mold, and therefore they have opposite draft on them.

Hi,

We have designed many, many such parts, and use 5 degrees as a 'rule of thumb'. Depending on how many parts you need to get out of the tool, and the contact area between the tool faces in this area, you can even use as little as 3 degrees - but it's risky.

I've found that most suppliers will recommend the absolute max. for just about anything: sheetmetal bend radii, part wall section, tool steel shut-off, draft angle etc. Experience shows that nearly all of these rules can be broken.

Regards,

Anthony

And some things I really don't need to know!

However, I always figure that to understand something about a process that you currently aren't using, will usually pay back in the long run. I don't know how many times I have read through something like this thread, knowing I don't do molds, but gleaning some little bit of info that does help me with something. Plus, I have, in the past, designed a couple parts that we had injection molded, and knowing something of the process helps immensely.

WT

"John Layne"

Bo,

I totally agree with you. This guy knows what he is talking about listen to him. We run a lot of polycarbonate, I wish everyone knew you could have such gaps with polycarbonate then we would get better venting. The newer close loop machines definately do a good job and I havent even had trouble with the hydraulic machines. They can be processed incorrectly and made to act like non closed loop if you dont knwo what you are doing.

Bo wrote:

Your mold maker / client isn't going to be very happy about the "feather edge" created by wrapping the shutoff around the radius on the lug. If that radius can't be removed from the part, I suggest designing the tool so it's easily repairable. I.e. "insert" that area of the tool, and make spare inserts, as the feather edge will definitely fail in production.

Yes, I did realize that the razor edge produced will wear quickly and ultimately fail, but I do need the radius there. I didn't really know what to do about it, however, your comment made me realize that there's something else that I can do about the problem to still keep the radius but prevent a razor's edge from being required. Thanks for that . . . I'll try to fix it.

'Sporky'

We use different hardnesses to prevent galling as well. Makes a big difference.

Mark B.

Some good rule of thumbs stuff can be found in Bill Tobin's books:

I also have links to good free resources on our site: at the references section. Most of these links are plastics design but some have tooling issues.

Mark B.

Spork, I can't tell for sure from the picture what the draft is on the right side of that cored out opening, but you have a shut-off on that side also. The wall looks 1 or 2 degrees. If not, disregard this message.

Good luck Mike Eckstein

Terminology! I'm not sure I understand you, but the draft on the right hand surface from bottom is 1 degree and also on the left hand surface it's 1 degree from the top. The shut off between those two cored out openings (where the drafts meet and cross) is 10 degrees.

You've gotten lots of good advice while I've been caught up in my work and unable to read the group. I would be much more worried about the feather edge at the radius than the angle of the shutoff.

I've still got my plastic product design standards from Mattel. They are over 30 years old and Mattel was pretty conservative about their tooling. (They wanted to build the tools fast and cheap and have them last for a reasonable number of shots.) They asked for an offset (from top to bottom of the angled face) of at least 0.010/0.015", with a minimum angle of 5 degrees. That meant that you needed more than 5 degrees on steps that were less than 0.114" tall. They also asked for 0.060" lands on the sides that you didn't want to flash.

We often use 3 degree shutoffs when we don't have room for five. You also don't need the 0.010/0.015" offset if you use more accurate locating features between the two halves of the mold, the parting line locks. (As I recall, taper locks are more accurate than bullet nose locks, but I'm a part designer, not a tool designer, and probably have the terminology screwed up.) Running different mold temperatures on the two sides can cause you to need more offset than normal.

Anyway, five degrees should be more than adequate most of the time. I would try really hard to get a flat at the radius that is at least 0.020" if the part is fairly small.

Jerry Steiger Tripod Data Systems "take the garbage out, dear"

Thanks, Jerry. I now have .015" flat instead of the feather edge or what I called a razor edge. That's all I can give it, and that's pushing some other limits of design for what I need the part to do. At any rate I'm a lot more aware of several criteria than I was before I began this thread, and have profited handsomely by the time that you and others have spent here. Many thanks to all once again.

Mark

Jerry Steiger wrote:

How big is the radius? The .015" flat will probably be strong enough if it grows quickly. At the very least, it's a hell of an improvement over 0!

Jerry Steiger Tripod Data Systems "take the garbage out, dear"

The way you have it now - is correct. We always as a rule of thumb used 5 degrees. But when the shut off is not very tall, we made sure that there was at least .005" angled gap when the shutoff steel was approaching each other (when the "A" side" met the "B" side.) If we didn't have at least this much, when the leader pins wore out and if the molding machine was wore out, there is a chance that the steel will collide and as soon as that happens, the steel will pickup/gall and you will have a spike of flash in that area (unless you are running the poly carb or other thicker plastics.)

We actually called out in our mold specs to have this draft. Cheaper corner cutting toolmakers or a proto-type moldmaker (that wants to be a production mold maker) would put straight shut-offs (no angle at all, maybe a .001" clearance) and the tool would run fine for the first shots and the tool company would get paid. Then after the tool runs for a few thousands shots, the straight shutoffs would gall and then the flash would start. You would send the tool back and they would blame the flash on you somehow and you would pay to fix it.

Anyway, the moral of the story is: always have angled shutoffs....

Dan Bovinich

22 years of moldmaking