Frame base curve measurement

Anybody out there know of a good way to reliably determine a frame BC? We try to match lens BC's to frame BC's (when necessary) with our surfaced lenses so they fit and look better.

I've tried to use a lens clock to line the three pins up on the frame front or back, but it's hard to keep the pins from sliding and measuring the wrong curve.

I've tried to measure demo lenses and they don't always fit right and sometimes are too flat or curved anyway. Sometimes I'll measure up to 2.00 D difference in curve between OD and OS demos simply because they fit better in one side than the other.

Our frame tracer on our Santinelli edger also has a habit of reading way too steep or too flat (verified by lens clock on the actual frame) so this isn't a great way either.

Any thoughts? Do they make a frame basecurveometer? I might be getting a 4T tracer, do they read frame curves pretty accurately?

Thanks!

Most frames are designed to accomodate a 6 base lens since this base curve can be used for a fairly large range of prescriptions. I only tend to experience problems with rather flat or steep curves, but this can be managed by bevel placement.

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Originally Posted by snowmonster

Anybody out there know of a good way to reliably determine a frame BC? We try to match lens BC's to frame BC's (when necessary) with our surfaced lenses so they fit and look better.

I've tried to use a lens clock to line the three pins up on the frame front or back, but it's hard to keep the pins from sliding and measuring the wrong curve.

I've tried to measure demo lenses and they don't always fit right and sometimes are too flat or curved anyway. Sometimes I'll measure up to 2.00 D difference in curve between OD and OS demos simply because they fit better in one side than the other.

Our frame tracer on our Santinelli edger also has a habit of reading way too steep or too flat (verified by lens clock on the actual frame) so this isn't a great way either.

Any thoughts? Do they make a frame basecurveometer? I might be getting a 4T tracer, do they read frame curves pretty accurately?

Thanks!

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Use a plasti PD stick and press it against the frame to take on it's curve and then use the clock on the pd rule it's a bit eaiser. It would be nice to havea framebaseometer^TM:D.

OPTIDONN - I know most frames do okay with 6 base lenses, but we like to do what we can to make that lens fit in the frame without looking ridiculous or popping out. This is especially true with today's flat frames.

Harry - that's brilliant! :)

I always put my thumb on the inside top of frame,(as you see your inside thumb is a perfect base curve GUIDE as it goes from flat base to 10 base)and use your thumb as the guide).Plus it fits perfect with width of clock.hope this helps:D:D:D:D

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Originally Posted by snowmonster

OPTIDONN - I know most frames do okay with 6 base lenses, but we like to do what we can to make that lens fit in the frame without looking ridiculous or popping out. This is especially true with today's flat frames.

Harry - that's brilliant! :)

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Base curve may not always be the culprit for lenses "looking ridiculous or popping out". Bevel placement should be a bigger concern. For instance on certain plastic frames have an area on the back of the frame front towards the temple in which frame manufacturers often add extra plastic as a way to create additional support (at least I assume that it's there for that reason). If the bevel placed too far forward the edge thickness can press there and cause the frame to flatten out. In some cases thinner lenses can "bow" out from the center of the frame due to a poorly calibrated edger or tracer. Those are just two common examples. There's a 1001 things that can cause a lens to sit poorly in the frame. Obviously the first step would be to select a frame that would work well with that RX. Then there is bevel placement, equipment calibration etc. etc. Selecting lens base curve based on frame compatability is not always the best choice, though necessary in some instances. I do get what you are trying to say. More than a few stylish frames just don't seem compatable with many RX's.

they used to make metal frames for high minus lenses,very wide bevels, and flat, haven't seen them in some time, I know Marchon had one. I agree with a couple of the other respondents that controlling the bevel the most important factor in keeping lenses fitting properly in frame, and looking good. One of the most important times a bevel needs to be put more towards the front of the frame is when you are cutting a high plus lens to fit into a magnetic clip frame.

we use a 4t and it is sweet with curves. Also on your edger if you have a base curve setting for the bevel us it on all frames instead of changing the base curve of the lens change the bevel of the lens to match the frame, and make sure the A measurement is dead on, if it is to big with thin lenes you will get the bowing effect

Before buying the 4T tracer, check out the new Rae tracer from GerberCoburn. I can trace wrap frames automatically and does a great job on measuring base curves of frames. I is also available as a Rae Plus with a dropdown screen to see tracings and with shape modification capabilities.

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Originally Posted by APV Optical

we use a 4t and it is sweet with curves. Also on your edger if you have a base curve setting for the bevel us it on all frames instead of changing the base curve of the lens change the bevel of the lens to match the frame, and make sure the A measurement is dead on, if it is to big with thin lenes you will get the bowing effect

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Yeah, our edger has those settings and we use them too. But it measures the BC of the lens weird as well. If we know the lens has a TC of +8.01, the edger will scan the lens in as a 9 base or 6 base or something weird like that. The funny thing is that most of the time it comes out good.

I just think it would be better if we knew the frame curve prior to surfacing to allow us to modify the lens BC a little.

sometimes too the lens is a little too big and if you take down the "A" it'll fit better and not pop out. Also, nice to pinch the frame down a little on the "B" to make it hold better.