Blacksmithing
and Cutlery
by Gérard HEUTTE Home
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Mosaic pins making
Introduction
These pins are made of a tube in which are inserted rods or tubes of different materials, shapes or sizes. Everything is sealed with glue or resin. Once mounted, the ends polished reveal a pattern. These pins provide a decoration for handles. They fit well with file work.
See opposite example of mosaic pin.
The majority of the pins use the contrast between gray and silver (steel, nickel, aluminum) and gold (bronze, brass) metals. The resin is generally black...

For use, provide a length of 15 to 25 mm (thickness of the handle) by pin.
Choice of elements
The elements are of two types:
> The external tube containing other elements. Choose it with a sufficient diameter. Personally, I use a diameter from 3 to 6mm.
> Inserts. Almost everything is usable in terms of shape and size ... The simplest are rods and tubes, but square sections (hard to find) can be used...

About matter, all the classics are usable: brass, bronze, copper, steel, nickel, aluminum...

Think also of recycled materials: Electrical wire (copper), stiffener of suspension files (steel), iron wire ... All that in small section can be used!

For supply, a variety of ways:
> DIY stores. Not much choice, but not too expensive.
> Recovery.
> Models Shop. Good choices, varying prices.
> Suppliers of metal materials.
Design
One of the difficulties of mosaic pins is to find the right fitting between the different elements available (tubes and inserts) with the respect of two rules:
(1) Avoid unsightly gaps between the inserts.
(2) Inserts must fit into the tube gently.

To achieve this, two approaches:
Rule of thumb: Try the assembly considered and see the result. A possible gap between the inserts can be detected during assembly. Positioning in the tube allows to see if the internal diameter is right.
Rational method: Start with a pattern and determine the dimensions of the tube and inserts. Several templates are provided below with the associated formulae.
Templates
The templates listed below allow proper assembly. They can be used in two ways:
(1) The internal diameter of the tube is known. The size of the inserts is calculated. Of course, the probability of arriving on sections with common dimensions is almost zero! The calulated values for the inserts should be round down.
(2) The diameter of one insert is known. Then the dimensions of the other inserts and the internal diameter of the tube are calculated. Again, the probability of arriving on common sections is almost zero! The calulated values for the inserts should be round down and the internal diameter of the tube should be round up.
The rounded values above are necessary to make an possible assembly with minimum gaps but a gap nonetheless! Warning: Without gap, assembly will not be possible.

Template #1

Formulae:
A = 0.5 x T      B = 0.6666 x A
Possible applications:
T=2.5    A=1.2    B=0.8
T=5.1    A=2.5    B=1.6
Template #2

Formulae:
A = 0.4641 x T      B = 0.2240 x T      C = 0.1547 x A
Possible applications:
T=2.4    A=1.1    B=0.5
T=4    A=1.8

Template #3

Formulae:
A = 0.4142 x T      B = C = 0.4142 x A = 0.1716 x T
Possible applications:
T=4.4    A=1.8    B=C=0.7
Template #4

Formulae:
A = 0.3702 x T      B = 0.3775 x A      C = 0.2596 x T
Possible applications:
T=4.4    A=1.6    B=0.6    C=1.1

Template #5

Formulae:
A = C = 0.3333 x T      B = 0.3544 x A
Possible applications:
T=4.6    A=C=1.5    B=0.5
Template #6

Formulae:
A = 0.2767 x T      B = 0.4466 x T
Possible applications:
T=4.1    A=1.1    B=1.8

Here is an Excel file to download with the different templates and the associated formulae to be able to experiment your own combinations:
mosaic pins templates and computation
Choice of resin
For bonding of the rivet, an gkue or a solid resin is chosen. Several points to be considered:
> Strength: The resin maintains the various elements.
> fluidity: This is a fundamental point. The resin must be able to easily fill any gap and facilitate the removal of bubbles.
> Life pot: This is the time available to use the resin after preparation and prior to polymerization.
> Toxicity: Beware of contact with skin and eyes. Do not breathe above the glue or resin (because of the solvents, sometimes very volatile).

Among the choices:
> Two-component epoxy glue. The epoxy glue becomes fluid with heat, but is still limited (in my opinion) in terms of fluidity. A temperature of about 80°C is fine. Prepare the glue in a pot and then put in a boiling water bath.
> Epoxy or polyester resins for encapsulation are very good because very fluid.
> Cyanoacrylate glue. Note that the cyanoacrylate glue darkens in contact with brass.

The products I use are:

Resin for encapsulation and its hardener

Dye of "ceramic paint" type

For the above resin (polyester resin for encapsulation GTS PRO Soloplast), the hardener dosage is 1.5 to 2% of the final mass! This makes very little when the hardener resin mass is about 20 grams! With a conventional balance, accurate to 1 gram, it is impossible to correctly dose the hardener. I circumvented the problem by weighing on a very precise balance drops of hardener: 20 drops weigh 0.52 grams! In practice, it requires 7 drops of hardener for 10 grams of resin.

The preparation of glue / resin will be done in a disposable container (plastic cup) following the manufacturer's instructions. If necessary, add a dye into the resin before adding the hardener. Mix well and avoid making bubbles.
If necessary and if the product allows it, add solvent to increase the fluidity.
Pin assembly
The assembly of the mosaic pin is a rather delicate operation. Here are some tips:
> Working with fairly short lengths like 100 to 150 mm. With big lengths, the assembly of rods can twist.
> Use inserts a bit longer than the tube for easy handling. In general, I have a margin of 5 to 10 mm.
> First put the peripheral elements in the tube, then the central elements.
> Avoid twisting because the inserts can be brittle, especially in small diameters (1 mm or less).
> Deburring the inside of the tube, to facilitate insertion of the rods.
> Do not squeeze the tube in a vice (risk of crush).
Assembly methods
There are many ways to assemble the mosaic pins. The inserts must be put in place in the tube and the gaps must be filled with resin.

Here are the methods I've heard about:

(1) Injection from the bottom: The tube should be prepared by forming a small funnel at the top of the tube with paper and adhesive. Then, place the inserts in the tube. The resin is injected from below through a syringe and a flexible tube (previously filled with resin). Stop when the resin overflows from above, into the funnel.
Disadvantages: You have a huge reserve the right diameter hose.
Caution: Always use a syringe, do not suck with your mouth! ! !

(2) Drawing up by the top: Inserts are placed in the tube. The bottom of the tube is immersed in the resin that is drawn through a syringe and a hose connected to the top of the tube. Stop when the resin reaches the hose.
Disadvantages: You need a reservation of the right diameter hose. The resin can flow from the bottom after pumping.
Caution: Always use a syringe, do not suck with your mouth! ! !

(3) Simple gravity: The tube should be prepared by forming a small funnel at the top of the tube with paper and adhesive. Then, place the inserts in the tube. The resin is poured from above into the funnel.
Advantages: Ease of implementation. Few consumables, moreover easy to find.
Cons: The resin can be difficult to flow into the small gaps. Bubbles or even air-filled sections can stay at the bottom of the rivet.

(4) Prior filling of the tube: Prepare the tube by forming a small funnel at the top of the tube with paper and adhesive. The bottom of the tube is clogged with adhesive. The tube is partially filled with resin. The inserts (held together by rubber bands or tape) are introduced gently into the tube. At the end, the resin will overflow into the funnel.

Advantages: Ease of implementation. Few consumables, moreover easy to find. Good results in terms of quality.
Disadvantages: Not always easy to keep all the inserts and in good position for insertion into the tube. Practice and habit can reduce this minor inconvenience.

This is the method I use and I describe in detail here.
A method in practice
Here are some practical details and pictures for the implementation of the method by prior filling of the tube.

For equipment, obtain:
> Paper and adhesive tape.
> A board with blind holes of the outside diameter of the tube. It will support the tubes during assembly.
> A pot to prepare the resin (yogurt pot or plastic cup) and spatula (ice stick) to make the mixture.

Then do as follow:
> Cut the inserts and the tube to the right length. In general, I cut the tube 1 cm shorter than the inserts.

On the photo against: The elements.
- On the left and at the center the inserts
- On the right the tube.
> Group the inserts. The tube (or a short section) can be used as a guide. Prepare the tube by making the funnel and close the bottom with tape.
   
> Prepare the resin by mixing it with the hardener. Proceed gently to avoid creating bubbles.
(A) resin (B) The dye is added (C) The hardener is added (D) Mixing gently.
   
   
> Pour the resin into the tube.

> Gently tap the tube to make up any bubbles.
> Slide slowly inserts into the tube by cutting the elastic as you go.
> Ideally, a small passage in a vacuum chamber removes the bubbles and fill the areas where the resin has difficulties to penetrate (small spaces). It is not mandatory, but it helps avoid unpleasant surprises!
> Wait for the hardening time for the resin.
> Remove the funnel and adhesive. Cut the ends. It is done!
Some achievements

From left to right: Model #6 - Model #3 with insert in tube of 2mm - Model #2 - Model #4