Quick and Dirty Way to Make a Pattern or Mold of a Curved Mirror

By far the easiest way. GA from me. Strength is added by using garden hose, thick rope, wooden slats, retic pipe, rolled newspaper, cardboard tube, whatever is at hand. Release agent is cooking oil. Easily cleaned off after. With fibreglass there is too much that can cause a catasthophe and negate the sale.
Jim

Agree. Bandages would work as an excellent binder. Like the way they used to cast/set broken bones.

Sets fast, little mess, easy to clean up.....

Yes indeed. I forgot about them. I used them once to remodel/repair some ceiling cornice, set quickly and made a strong substrate to mould the top layer to the shape of the cornice.
Jim

For hobby type casting I think there are two main companies for plastic type molding. I can't recall either at the moment but I think Hobby Lobby carries both.

A friend took some police academy CSI courses. I think the mold material that they use is called dentalstone. At the time I looked it up on the internet and it was available to "normal people".

Youtube is your friend. "Casting" and "mold making" should take lots of hits.

Someone in the CR4 community should be familiar with fiberglass molds and release agents for boats and/or car panels.

Plaster of paris is common but what you are doing is large enough that I suspect the plaster will crack and fall apart.

Once you have these molds what will you do with them? The lens part is pressed glass and probably out of scope for your workshop. The back is probably just a parabola.

Thank you very much. Your answer encompasses what I want, which is to be able to "re-create" one later, with whatever - for whatever.

If I have that curve, from the center to the edge, I have all I need, and it's lightweight and takes little space to store.

Thank all of you, as usual!

#9

You are welcome.

Don't forget to take some basic measurements like edge to edge distance of the reflector and the distance from the center of the reflector to where the reflector ends (the total depth of the reflector along its centerline).

Don't forget also to measure the relative position of the lamp. If the reflector is parabolic, which would seem best for a searchlight, the lamp will be at the focal point of the parabola.

Good catch!

If you go down that path make sure you keep the compass vertical ( if the mirror is level that is ).

I gave you a GA. Your idea was better than mine!

May be too late, but thermoforming comes to mind.

Depending on the size, you may be able to use the wife's oven/broiler.

Put a sheet of acrylic/ABS/PVC/ or just about any thermoplasitc in a frame, soften it in an oven until it sags, then drape it over the lamp dome.

I'm sure instructables of You Tube can guide you.

If not, PM me and I'll walk you through.

A little off topic on the reason why they having been improved upon the mirror is that it's probable a parabola.

Plaster cast it with cheese cloth and wood. Use that later with fiberglass and resin as the mold and make a master.

I'm assuming that you have already undertaken some means due to the time frame you mentioned. I would avoid plaster of any sort due to weight and it's proneness to cracking. Fiberglass can be messy and expensive and damage to your original would be costly. A simple rather inexpensive means would be to cut a board to the rough min and max depths of the reflector minus 3/4 to 1", put a number of nails sticking out on the curved side by 3/8 to 1/2", put down kitchen wrap along the main diameter, buy some plastelene or modeling clay or a product like Freeman Pattern-Maker RenPaste-569 or 8281 and press gently down to achieve full contact and encompass the nail heads and allow to set or harden if epoxy or with the clay pull up the board/clay with the plastic wrap and you should have your template. You could then trace that outline onto another board for a more permanent template. At one time sand molders would use such a template such as this as a "sweep" to make one side of the mold. You can find many products for making copies of items on the Freeman Pattern-Maker Supply website. Kindt-Collins used to be another good source.

Would one (or more) of these do it?

Another way is to use 2-part expandable foam, mix and pour type. Follow the instructions for whatever they choose as a release material. (Liquid or sheet based).. You will need a way to keep it compressed to what ever density required .THen use what ever material available as a female mould. Used it the past as a way to take-off forms and patterns when building complex curves in aircraft and boats. THe other methods mentioned all have merit, just whatever you are comfortable working with , and the tools available. Let us know how it goes!!