RE: Keltool Lead Times

From: Connelly, Rob - BDRC (
Date: Fri Feb 14 1997 - 15:00:27 EET


I have used Keltool on a number of projects now, and I'll do my best to tell
you what I have experienced.

>Keltool states that their "Normal" lead time is 3-4 weeks.
>Has this held true for you?

I have never requested their "normal" lead time. I have paid the fee for
the Super Rush on every occasion. I have found that the time from my
masters hitting FedEx to 3D-Keltool inserts arriving here FedEx has been
about 8-9 days elapsed time (that includes their weekend downtime) with the
Super Rush service.

>Has anyone had any experience with small ribs and
>features in a Keltool cavity?

Yes, their process has reproduced any and all features that I have sent
them, and our parts are little medical goodies with tiny features. I think
you will be impressed.

>Keltool has told me that a 4:1 ratio of height to width must be
>maintained on small features. Does this mean that a standing
>rib 6mm wide can only be 25mm high? How small of a rib is

That is what they tell you, yes - and I imagine that means they are not
liable if they are unable to reproduce those features. It poses a yield
issue, given that they have to pull those fragile features out of a rubber
mold when the 3D-Keltool mixture is not fully sintered. Unfortunately,
EVERY job I have sent to them has violated that rule - and they wisely
cautioned me about it - but they have come through on each occasion. In one
instance they had to try several times before they pulled it off, leading to
a delay that was certainly unavoidable. You will reduce the probability of
a failure by polishing your master in the draw direction to eliminate any
evidence of stair-stepping.

>Does Keltool reproduce sharp corners (both internal and external)
>or does it add a radius to these features. If so how much?

Although I have not measured radii before and after, it is evident that
their process reproduces internal and external corners exceptionally well.
 The material is very fine-grained, and it is vibrated into the rubber mold,
so corners are completely filled, without rounded edges.

>How well does Keltool shutoff against itself. If I create bypass
>shutoffs of 3-5 degrees will this be sufficient?

It seems to be good practice to leave a tiny amount of stock on any shutoffs
and to perform some sort of secondary operation to bring them within the
spec that you need. Bypass shutoffs in particular will be sensitive to any
distortion in the metal (there is very little distortion, but some.) An
excellent way to do this is to EDM the pieces together. I just used that
method on a job that had a complex set of interlocking bypass shutoffs, and
the resulting molded part had no flash whatsoever. The draft was from 1-5

Try it out! But remember that if you violate the rules you MAY end up
machining the tool conventionally. Thank goodness I have not had to do that
yet, after about 14 projects. I have been very pleased, indeed.

 - Rob
Rob Connelly
Becton Dickinson Research Center
21 Davis Dr.
RTP, NC 27709
(919) 990-2263

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