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Drilling slotted holes in rubber

Drilling slotted holes in rubber

(OP)
I am working on a project where we need to field drill slotted holes in a rubber gate seal. The rubber has a durometer harness of 60 to 70. Currently, round holes exist in the rubber seal which are used for retaining to the structure. In order for fit up, we need to slot the holes by approximately 2 to 4mm. Our thoughts are to use soapy water on both the rubber and drill bit and use a die grinder to elongate the holes.

Does anyone have any recommendations for how best to field drill the rubber?

Thanks in advance.

RE: Drilling slotted holes in rubber

Can a slotting punch be used, similar to what is used in gasket making or leather craft? Rubber does not machine well, unless you can stiffen it up by freezing. You could see some success with a die grinder, but it's not ideal, to say the least.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Drilling slotted holes in rubber

(OP)
Thank you for the advice. A slotting punch may be possible, however, we would have to find one that would work with the seal geometry. Freezing it may also be difficult as this will be done in the field with above freezing temperatures.

When you say that a die grinder is not ideal, why exactly do you specify that?

RE: Drilling slotted holes in rubber

Any form of machining is difficult with elastomeric materials. Grinding, drilling, milling, etc. You might have some success with an abrasive point or a cutting burr in a die grinder. Also, any form of rigid material that you can clamp to the rubber to stiffen it while grinding/cutting/machining will help. You don't happen to have a sketch of the cross section of the seal with detail where the slots need to be, by any chance?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Drilling slotted holes in rubber

(OP)
I believe we could clamp something to the seal to stiffen it. See attached for a shape of the seal. The seal is 102mm long and is 14.2mm thick. The slots will run in and out of the page when looking at the sketch. I do not know the dimension from the edge of the seal to the center of the hole, but I would estimate it to be approximately 38mm.

RE: Drilling slotted holes in rubber

At first glance it looks like an ordinary slotting punch would work. The slot does not encroach into the bulb portion, is that correct?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Drilling slotted holes in rubber

(OP)
You are correct, the slot would not encroach on the bulb portion. Possibly the punch is the best option. Thank you very much for your input.

RE: Drilling slotted holes in rubber

I have had some success in the past using a sanding drum that is smaller than the slot width in a die grinder. It will be a slow process though. If your slot will end up being very long you might consider also using a saw to cut the center line out from your existing hole to help keep the die grinder on track.

RE: Drilling slotted holes in rubber

(OP)
Thank you for the advice. Thankfully the holes don't need to be elongated by a great distance, only about 2-4mm. However, there are multiple holes that need to be completed.

Thanks again!

RE: Drilling slotted holes in rubber

When grinding holes in rubber with a high speed grinder use plenty of lubricant even water, also because of the way the rubber particles drag on the abrasive, the cut will very often be at 45* to the desired direction unless counter pressure is added.
B.E.

You are judged not by what you know, but by what you can do.

RE: Drilling slotted holes in rubber

A big soldering iron with a slot-shaped tip should work nicely.

Or two passes with a tire grooving tool, which is basically the same thing with a half-slot shaped tip, no custom machining needed.

Keep a fire extinguisher handy.


Mike Halloran
Pembroke Pines, FL, USA

RE: Drilling slotted holes in rubber

I worked with a company www.rubbersheetroll.com that used to recommend soapy water in the process to reduce the friction/shape distortion.

RE: Drilling slotted holes in rubber

(OP)
Thank you for the advice, greatly appreciated!

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