Official Luthiers Forum!

Whats the best tool to scribe a plan onto a lexan (Polycarbonate) sheet?

Is an exacto knife too fine? Have you found the perfect tool? I'm wondering if that would leave ridges along the cut and i should use some type of scraping tool... suggestions?

Thanks!

I score them with a very sharp awl.

_________________
It will probably be alright.

I have a bunch of various awls but the one I always go to is the General Tools Tungsten Carbide Scribe.


Sent from my iPhone using Tapatalk

I just put the Lexan over the plan and trace with a fine tipped permanent marker.
Rubs out with alcohol if you make a mistake.
Constantly refer back to the plan as the outline is shaped (bandsaw/linisher/bobbin sander)

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Colin, I am assuming then you have no issue with the marker? I was thinking that maybe it would not last... but obviously you would not use it if that were the case.

All: I am thinking I will drill pencil holes in the template to be able to mark the brace positions. Any reasons not to bother? Do you find you typically adjust the bracing from one build to the next?

What I did was print a second copy of the plan (or copy it if it isn't in digital form) and then glue it to the Lexan with spray mounting glue. Then, like you suggest, small holes at the end of each brace to mark the brace ends and intersections. Like this:



(The big hole through the tongue depressor is just for mounting on the wall. )


Sent from my iPhone using Tapatalk

_________________
Insta - https://www.instagram.com/cbcguitars/
Facebook - https://www.facebook.com/cbcguitars

We use a high quality awl or machinist's scriber and French or ship's curves to accurately transfer the lines from paper plans to clear 0.090" polycarbonate template material. Lines scribed in the Lexan are highlighted with Sanford markers (just pass the tip over the scribed line...the ink will wick to the bottom of the line), and the excess is removed with alcohol. Top bracing gets scribed on one side of the half template, then the back bracing on the other (this avoids laying out the tone bars reversed from the plan).

Based on my own experience, I avoid using knives for this job, as they will cut plastic or metal curves as readily as they do other materials, and the quality of steel and the sharpened edge from the makers of new Exacto knife blades is at best inconsistent, requiring frequent resharpening. The sharp, fragile tip of the #11 blade usually needs a little honing to fix the hook seen from manufacturing.

In this shop, the two tools most often used for the template making job are the Blue Spruce awl (expensive...think well made Italian shoes...just perfect and very elegant) and the Starrett 67B two point scriber, which is much more moderately priced, and a working person's tool found in many metal and wood shops. The steel in both is excellent, and we use these tools for all of our layout work due to the fine, uniform, durable tip.

In terms of the ships' and French curves that mimic the curves found in guitars and other instruments, there are several sets worth considering:

This Westcott set has three curves that handle most body curves (the three rightmost in the photo):

https://www.amazon.com/C-Thru-Ship-Curve-Set-6/dp/B000HEOHVC/ref=sr_1_1?ie=UTF8&qid=1479469421&sr=8-1&keywords=curves+ships

This ship curve is useful for tighter curves such as cutaways...combined with the set above, it covers most applications:

https://www.amazon.com/Art-Advantage-8830-Ships-Curve/dp/B0027AED7C/ref=sr_1_4?ie=UTF8&qid=1479469421&sr=8-4&keywords=curves+ships

This set of French cuves is very expensive, but gets a great deal of use in this shop:

http://www.sterlingtoolworks.com/store/#!/Sterling-Roubo-Curves/p/52063286/category=12516967

The Starrett 67B mentioned above:

https://www.amazon.com/Starrett-67B-Improved-Scriber-Two-Points/dp/B000VDTH32/ref=sr_1_1?ie=UTF8&qid=1479470683&sr=8-1&keywords=starrett+67B

The Blue Spruce awl mentioned above (ours is part of a set of three tools which includes a small, long blade marking knife and a larger knife....all in Gabon ebony):

http://www.bluesprucetoolworks.com/scratch-awls

Although we have a few older acrylic (Plexiglas, Lucite) templates, this material is much less durable than polycarbonate (Lexan, Makrolon, etc.), and is more difficult to work due to it's brittle nature and tendency to melt when sanded. We buy our polycarbonate template material from the local Home Depot in the largest sheet size available to minimize overall cost.

_________________
A constellation only takes shape when one maps the whole.
- Beth Brower

No issues with the marker, I drill holes for brace alignment, scribe lines for anything if required (back bracing, centre soundhole...) - as Woodie says, permanent marker highlights it.
I only make half a pattern, and mark all brace ends on that template (identifying left and right on back or front as appropriate - B1, B2,etc. if assymetric bracing.
Saves time, guarantees sym/metry.
Adjusments can be made after marking out workpiece if needed.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.