Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Machining accuracy with silicone rubber

Machining accuracy with silicone rubber

Machining accuracy with silicone rubber


Anyone got experience of CNC machining silicone. Using it as a gasket and we're not sure what sort of accuracy can be achieved? Would it be in the region of +/- 0.5mm? Will be using it as a gasket and it will be 15mm thick.

RE: Machining accuracy with silicone rubber

Dunno why you wouldn't machine a mold and mold that. You could try freezing the stuff to make it stiffen up, it will machine a little easier that way. Alternatively, use a grinding burr.

RE: Machining accuracy with silicone rubber

I imagine a mold would be expensive for 1 custom made piece of silicone?

RE: Machining accuracy with silicone rubber

Doesn't look complicated enough to be expensive - if you have a CNC mill already. Machine the mold in two pieces of aluminum with a couple of bolt holes to clamp it together, or one piece if you don't care about having the thickness held to a very tight tolerance. Cut a couple of vent holes, fill the cavity with RTV*, bolt it up and let it cure... The nice thing about silicone is you really don't need to worry about draft in the mold, nor release compounds, just have a fairly smooth mold surface and you should be good.

*https://www.mcmaster.com/rtv-silicone-casting-comp... - there are a lot more and probably cheaper sources out there, google/amazon etc.

RE: Machining accuracy with silicone rubber

Machining soft materials usually requires freezing them.

RE: Machining accuracy with silicone rubber

Try water jet cutting.

RE: Machining accuracy with silicone rubber

@iainuts - Cool, thanks for that.

RE: Machining accuracy with silicone rubber

You can't cut the illustrated step with a water-jet; you need to cut entirely through the sheet.
You could water-jet two flat pieces and bond them together.

... but it's MUCH easier to machine a stepped cavity in a block of aluminum, polish it, pour in RTV, and let it cure.
Self-leveling RTV probably wouldn't even need a cap/cover on the mold. ... and would cure more slowly if a cap is present to restrict uptake of atmospheric moisture for curing.

Two-part RTVs intended for molding would probably need a two-piece mold, and will cure more quickly than single-part RTV.

Mike Halloran
Stratford, CT, USA

RE: Machining accuracy with silicone rubber

I made a few special seals using acetal for the mold and a 2 part silicone with good results. Didn't measure it post bake, but it seemed like a perfect fit.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


White Paper - Strategies to Secure Connected Cars with Firewalls
White-hat hackers have demonstrated gaining remote access to dashboard functions and transmissions of connected vehicles. That makes a firewall a vital component of a multilayered approach to vehicle security as well as overall vehicle safety and reliability. Learn strategies to secure with firewalls. Download Now
White Paper - Model Based Engineering for Wire Harness Manufacturing
As complexity rises, current harness manufacturing methods are struggling to keep pace due to manual data exchanges and the inability to capture tribal knowledge. A model-based wire harness manufacturing engineering flow automates data exchange and captures tribal knowledge through design rules to help harness manufacturers improve harness quality and boost efficiency. Download Now
White Paper - What is Generative Design and Why Do You Need It?
Engineers are being asked to produce more sophisticated designs under a perfect storm of complexity, cost, and change management pressures. Generative design empowers automotive design teams to navigate this storm by employing automation, data re-use and synchronization, and framing design in the context of a full vehicle platform. Download Now
eBook - Simulation-Driven Design with SOLIDWORKS
Simulation-driven design can reduce the time and cost of product development. In this engineering.com eBook, we’ll explore how SOLIDWORKS users can access simulation-driven design through the SOLIDWORKS Simulation suite of analysis tools. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close