Drill Edge Thickness - Retail vs Lab

**successken** · 08-13-2013, 09:34 PM

We are currently having a debate on edge thickness for nylor mounts but mostly drill mounts. We have a policy that if the Rx is +3.00 to -3.00 the required material is Trivex, beyond this range a Hi-Index can be used. Polycarbonate we try to stay away from. The retail would like the final product to have the thinness edge thickness even if it means drilling a stock lens. The lab would like to produce a product that will not chip or crack so they have imposed a minimum edge thickness on all drills and nylor mounts. Do you have a required edge thickness for drills and do you have a different requirement for plus lenses versus minus? If so, what is it?

**Chris Ryser** · 08-14-2013, 06:10 AM

No thickness required for drill mounts, but to make a good groove you will need 3mm

**optimensch** · 08-14-2013, 07:36 AM

not all drill mounts are the same. some rimless styles require a minimum edge thickness or the lens won't be properly secured (due to post length eg.). In some cases the frames are quite stiff, no spring hinge temples, and a lot of pressure is transferred to the drill holes - increasing strain and chance of a break.

I find with trivex , in plus powers especially, you can go to a thinner edge generally.
in many cases i dont see what is wrong with a stock lens....whether a trivex or above a -2.50 (depending on lens size etc...) a 1.6 or 167.
We do loads of drill mounts with stock lenses, as long as you account for the type of drill mount, the patient's needs, rx etc....
But in the Litigious States of America maybe you need to be more on guard than in Canada.....

**Jason H** · 08-14-2013, 07:42 AM

3.0 seems a little thick. 2.4-2.5 is entirely reasonable with trivex especially. I don't buy into the bias against poly either, even with drill mount. Chamfer, use your plastic washers and make sure the holes are big enough to accomodate pressure mounts. Watch edge thickness on plus powers - you can often go thinner for drill mounts. You seldom drill a hole right on the edge.

**Pogu** · 08-14-2013, 08:07 AM

I would say 2.4mm ET, using a .75mm groove width.

Drill mounts really depend on the mounting, if it braces against the side of the lens or uses a notch I use the same 2.4mm. I prefer the 1.4mm X 3mm plastic compression mounts (Charmant, Sillouette, etc.) I find 1mm ET to be fine for them since the post is nominally 2mm (or more) into the lens, giving you plenty of thickness at the actual mounting point.

Also I do poly for drill mounts all the time without issue. Ensure sharp drills, chamfered holes, proper adjustment and your good to go. Trivex is still an upgrade and 1.67 is certainly a peach to process, but poly is a perfect basic material when handled correctly.

**jefe** · 08-14-2013, 08:35 AM

Originally Posted by successken

We are currently having a debate on edge thickness for nylor mounts but mostly drill mounts. We have a policy that if the Rx is +3.00 to -3.00 the required material is Trivex, beyond this range a Hi-Index can be used. Polycarbonate we try to stay away from. The retail would like the final product to have the thinness edge thickness even if it means drilling a stock lens. The lab would like to produce a product that will not chip or crack so they have imposed a minimum edge thickness on all drills and nylor mounts. Do you have a required edge thickness for drills and do you have a different requirement for plus lenses versus minus? If so, what is it?

I want to see at least 2mm where the drill holes are located. On nylor, with Trivex I'll do a 1.8 mm edge comfortably and have gone down thinner than that at times.

**Barry Santini** · 08-14-2013, 09:26 AM

Hell, depends on the plus Rx...Using trivex, and bushings, I have no problem with stronger plus having a 0.8mm FE, and outer drill hole thickness of 1.7mm.

B

**successken** · 08-14-2013, 06:28 PM

Thank you for the responses.

**Speed** · 08-14-2013, 06:37 PM

Careful when requesting minimum edge thickness for drill rimless. The edge thickness is one thing, the thickness at the hole in the lens, 2 mm in from the edge is another. The stronger the power, the more the difference. LMS suppliers have not yet gotten a handle on this. Many labs haven't either. Conversations are advised.

**WFruit** · 08-14-2013, 09:24 PM

From a lab perspective (though I've also spent about 7 years total of my career in a retail environment)

Grooved - Depends on material. "Standard" for Poly/Trivex would be 1.8~2.0. All other materials (including glass) would be 2.0~2.2. Thinner by special request might be possible, depending on frame and material. Note that most labs have edgers that will do the grooving as part of the edging process, and the machines usually also have a minimum that they want to put the groove into (yes, that can usually be overridden in the software and also usually shouldn't be). Grooving by hand is also possible, but the person needs to know what they're doing if it's going to be on a thinner lens. Personally, the thinnest I've ever grooved is a 1.3 Poly.

Drilled - Depends on material AND frame design. "Standard" for Poly/Trivex is 1.5~2.0. High Index (1.60, 1.67, 1.74) is usually 1.8~2.0. But it also depends on the frame design. Is it a compression mount? Screw into posts? Nut and bolt? Nut and post? Or one of the other funky wacked out designs I occasionally see? Is it two holes in the lens, or a hole and a notch? Minimum thickness really isn't delegated by cosmetics, but by how thin the lens can be and still have the frame be able to be put together and stay together. AND don't forget there is also a maximum thickness beyond which frames can't be put together.

Originally Posted by Speed

The edge thickness is one thing, the thickness at the hole in the lens...is another. The stronger the power, the more the difference. LMS suppliers have not yet gotten a handle on this. Many labs haven't either. Conversations are advised

But, edger companies have. Or at least some have. We use ME-1200's, and for all drill jobs, it will measure the thickness at the holes, as well as the front and back curve of the lens where the holes will be, so the holes will be drilled "straight."

And since the thickest part of a lens is related to, and usually based on/derived from, the minimum thickness required/requested for the thinnest part of the lens, if you know/can do/feel like doing the math, you can work out what the thickness will be where the holes are.

I will also say that I've never seen an order request a specific thickness at the drill holes. It's always edge or center, and I'll wager it's due to cosmetic considerations only.

Conversations with the lab to make sure everyone's in the same book, same chapter, same page are NEVER a bad thing and, as a lab person, ALWAYS highly recommended.

**cmhargrove** · 08-15-2013, 12:09 PM

Originally Posted by Speed

Careful when requesting minimum edge thickness for drill rimless. The edge thickness is one thing, the thickness at the hole in the lens, 2 mm in from the edge is another. The stronger the power, the more the difference. LMS suppliers have not yet gotten a handle on this. Many labs haven't either. Conversations are advised.

I agree with Speed. You are asking about two main considerations ("edge thickness" on plus, and possibly "center thickness" on minus), but the other processing variable is "average thickness." On a low plus power drill job, the average thickness is possibly the most important variable to control, but takes a little experimentation from your lab to determine their capabilities.

On Poly / Trivex, we use min CT and ET of 1.5, and average thickness around 2.0-2.3. These three variables together help you to triangulate the most beautiful, structurally sound drill mount lenses. So, it will take a little experimentation on your part but that's what we use (and we have a very robust drill mount business).

Hope that helps.