Flat Lap Discs

Selection

Diamond discs for flat laps are expensive and the temptation is to buy as cheaply as possible. There are a number of relatively inexpensive sintered and bonded diamond steel base discs. These are acceptable up to about 220 grit, but the finer grits can leave deeper scratches. It seems to be the grit size is not closely controlled, allowing coarser grits into the bonding process. My experience is that the scratches left by the coarser grits can be worked out with more expensive, but higher quality discs of 400 grit. This allows the finer smoothing and polishing grits to produce unblemished surfaces.

Maintenance

The lap wheel needs to be free from any grit. The disc can be visually inspected for any large particles, but this will not be sufficient for smaller particles. The cleanliness of the disc can be tested by turning on the water supply to the slowly spinning disc and placing the flat of your hand onto the surface. Any grit discovered needs to be cleaned from the surface. This is especially important when using flexible smoothing and polishing discs. If you do not, you will wear away the surface of the disc, leaving bare spots.

Similarly, when grinding/polishing with a lapping disc is finished, you must ensure the disc is clean and free from any rough spots. This can be tested with your hand on a slowly turning disc. If there are grains of glass that are not cleaned at this stage they will become imbedded in the disc and reduce its useful life. Flush the surface of the disc while slowly spinning until no rough spots, especially on the outer rim, can be felt.

Then the disc can be lifted off the wheel and the bottom surface cleaned of any debris before putting aside to dry. The storage of he discs should be dry land keep dust and other contaminants off the discs.

It is not good practice to leave a disc on the wheel for longer than it is being actively used. Rust can form on the wheel and it allows debris to collect on the disc. Anyway multiple disc changes are required to go to finer grits and polishing discs, after the shaping is completed.

There are a number of good videos on HIS Glassworks which discuss the use and maintenance of grinding and polishing discs.

Is it Possible to Make Flat Laps Yourself?

A flat lap is a horizontal spinning disk to grind and polish flat surfaces onto the fired glass piece.

Many desire one of these but are put off by the expense and sometimes the space they occupy.

There is a do-it-yourself alternative that I have used.

This is to use potter’s wheels as flat laps. Table top versions are useful as they are moveable to a storage shelf when not in use. Mine was kept on a shelf until it was taken outdoors to avoid water spray indoors. They do require some adaptations and have limitations. But the great advantage is lower cost.

There are new table top ones available from £135 with a 25cm/8” turntable. This is the maximum size. They often come up second hand on ceramic and local buy and sell sites for even less.

Adaptations are required. These include:

The wheel is surface is aluminium, so a magnetic surface must be applied, as the metal discs rely on magnetic attraction to stay in place. Magnetised sheets with self adhesive backing are available to be cut and stuck to the wheel.

A water supply needs to be fixed. This can be a removable reservoir with an adjustable flow valve, or a hose from the standard water supply with a controlled flow.

The water catchment basin around the wheel does not have a drain. You can live with that and interrupt the work to empty the basin as required. Alternatively, a hole can be drilled in the basin and a Loc Line or similar system can be fixed to drain into a bucket. The waste water should not go into a drain, because the sediment will eventually block it solid. A recirculating pump is also a bad idea, because it will distribute glass grit along with the water onto the disc, and cause scratches when using a finer grit disc.

Discs must be acquired. Consider metal discs with a progressive range of grits from around 50, and doubling the grit number (halving the grit size) to around 400. I normally start with a 100 grit disc, as the coarser grits are really only for removing large amounts of glass. 100 grit can do the same job as 50 grit, but requires longer.

Inexpensive steel disks are available. However the quality of grit sizing is not always accurate, making the use of the cheaper discs with grits above 220 inadvisable. The finer grits and smoothing pads need to be of a higher quality and their expense will be justified by the lack of gouges in the later stages of fine grinding and polishing.

If you use larger or smaller discs than the wheel, you need to mark the centre on the magnetic pad, to be able to easily centre those smaller or larger discs. Of course, the smoothing and polishing pads are on flexible backings and cannot be larger than the wheel. Only the steel backed discs can be larger.

This picture is an example of my potters wheel adapted as a flat lap. The magnetic pad has been attached to the wheel, and the water supply hose and flow valve are also attached.

Rear view with grinding disc in place 

Limitations

There are limitations to this make over of course.

• The wheel surface is 25cm/8” dia. A steel plate could be attached to make the surface 30cm/12”, although centring it may be difficult.

• The speed is easily adjustable, but the top speed is around 300rpm

• The the basin is 32cm/13” diameter and its edges rise above the wheel, limiting the size of items that can be worked.

• There is no drain from the surrounding waste water basin, so drain holes may need to be added.

In spite of the limitations, this worked well for me for several years, until I had the need to flat lap large numbers of items. For those with moderate lapping needs, this is a good, low cost piece of equipment.

Peptides as a Glass

 Peptides as a glass. Thanks Susan Walpole for the link to a YouTube video.

youtube.com

A glass that builds and heals itself

Researchers have discovered that a peptide, when mixed with water, can self assemble into a rigid 

Crate for a Travelling Exhibition

 

I was accepted along with others on the basis of a proposal to exhibit with a travelling exhibition organised by the Scottish Glass Society.

This will be packed and unpacked by other people at least four times during the exhibition year. My experience with helping to pack up the Collect work exhibited by craftscotland showed me the need to prepare the packing properly.

I decided to build a crate with custom fittings to cushion the work from any damage. I felt when I finished that it was such a simple arrangement that others may benefit from a description of what I did.

The crate can be made from a variety of materials, of bourse, but wood is easiest for me.  I used some plywood offcuts to form the base and sides.  The ends were formed from 3 ply plywood with 19 by 45mm timber cut and nailed to it.

The side rail does not have to be so large as I made it - just too lazy to cut it down. The side rail allows the top to be screwed to the sides holding them from expanding or bowing with the pressure of the packing materials.

I then cut 50mm thick polystyrene sheets to fit the case. These were attached together with "U" shaped copper wire stuck into them. The shape to fit the glass was cut with a heated cutting tool. It is a bit smelly and smokey, but does the job. When the shape for the glass was formed, a 10mm sheet had a collar cut out to go around the rim of the glass.

Note that the packaging is also numbered so that each piece is put back into the crate in the order required for transport. When the base layer and cradle for the glass are placed in the bottom of the crate, the glass is added.

Now the crate is ready to have the wooden part of the work packed. This shows the piece with the glass in the wooden cradle with the packaging around the "slipway".

The packaging for the "slipway" is put into the crate separately from the glass and packaging. You can see there is a layer of polystyrene between the glass and the wood.

Then the "slipway" is inserted into its cradle.

The polystyrene had holes made with the hot cutting tool to correspond to the supports for the glass. The holes are larger than the supports, so there is no pressure on them during transport.

Again the packaging is numbered. The final packing pieces are to be added now. Still each has its number!


The major pieces of packing are now added ready for the topping out!

Next add the essential tools and spares. In this case the tool is a two way spirit level so the piece is placed horizontally and level.

Then there is the necessary photo to show how the piece is to be displayed.

Finally the list of contents and instructions on installation.



Now the lid can be put on and screwed down. Note the locating marks on the lid to show how it fits without having to run new pilot holes for the screws. The screws to be removed are noted with an "X".





Screwing together to be solid and ready for delivery.





If the instructions are followed everything should be secure for delivery to the buyer!

P.S:  It came back in one piece. Unfortunately it did not sell during the exhibition, but it did later.

Is Vertical Crescent Attachment Possible?

“I want to tack fuse [6mm thick crescents to] stand erect...[on] a base. I need help thinking this through. … Is there a way to fuse them erect without forming a puddle of glass?”

It is correct that at tack fuse the crescents will deform. It is, after all, above the slump temperature.

You could use fibre blanket packed between the crescents arranged in a fan formation. This requires assembly on the kiln shelf. If you allow them to touch at the pivot point, they will stick to one another during the firing.

Use a sinter firing. It will be something like:

• 65°C/ 117°F to 670°C/ 1236°F for 6 hours.

• The anneal soak should be for 5 hours at the appropriate temperature. The associated cool is at 11°C/ 20°F to 427°C/ 800°F, 0’;

• 20°C/ 36°F to 427°C/ 700°F, 0’;

• finally at 52°C/ 117°F to room temperature.

This arrangement and firing will enable the crescents to be securely attached to the 6mm base with a minimum of distortion.

More information is available in my e-book Low Temperature Kilnforming, available from:

• Bullseye

• Etsy

• and   stephen.richard43@gmail.com

Stress Testing - How?

 This is a presentation I gave a while ago on why and how to test for stress without risking the piece, that is, non-destructive testing.

How can I Release Glass Trapped in Casting Moulds?

How to get stuck glass out of a reusable mould?

The material is important to the method of removing stuck glass.

• Metal expands and contracts more than glass.

• Ceramic expands and contracts less than glass.

Mechanical methods

• Metal moulds can be hit relatively hard to break the contact between the mould and glass.

• Ceramic moulds should have only gentle taps, as they are more fragile than metal.

• If the glass is stuck, but moveable within the mould. It may be possible to wiggle the glass and mould against each other, which after a time may wear away the contact points and release the glass.

• Do not try to pry the glass from the mould. It is likely one or the other will break.

• Destructive method is to break the mould or the glass, which ever is the least important.

Contrasting temperature methods

Drape over metal –

• The metal contracts more than the glass, so placing the two in the freezer is one possible approach.

• Alternatively, heat the glass with hot water

• A third method is to place the drape upside down in the kiln and take it up to slumping temperature. Peek to determine when the glass has relaxed enough to be free from the mould. If the release temperature is above the annealing point, anneal again as before.

Drape over ceramic -

• The glass contracts more than the ceramic, so heating the glass with hot water may provide enough expansion to release from the mould.

• Or place the drape upside down in the kiln and take it up toward the slumping temperature. Peek to determine when the glass is released and skip to the anneal and cool process.

Slump into metal -

• The metal contracts more than the metal, so heat treatments will work best.

• Apply hot water to the metal until the glass is freed.

• Place the mould upside down on short posts and fire until the glass drops out. If the annealing temperature is exceeded, anneal again.

• Bang the metal mould with a rubber mallet. This risks breaking the glass, of course.

• Freezing only tightens the hold of the metal to the glass.

Slump into ceramic -

• The glass contracts more than the ceramic, so cold can work.

• Usually, glass sticking to a ceramic mould is a result of insufficient coverage of the mould with the separator.

• Placing the mould and glass in the freezer for a few hours may allow the glass to contract enough to be freed when taken out.

• Place the mould upside down supported on short posts. Set the firing to go to fusing temperature. Monitor with quick peeks from the slump temperature at regular intervals. When it drops, skip to the anneal process.

• Firing to a high temperature does not always release all of the glass.

Using adequate and appropriate separators to avoid trapping the mould or the glass need to be used to prevent the need to employ these release methods.

How can I Insulate Reactive Colours?

Sometimes the ideal colours for your project are reactive with each other, but a reaction line, or area, is undesirable.

Bob Leatherbarrow has demonstrated the possibility of avoiding the reaction. This works most clearly when using frit to blend one colour into another. Lay down the first reactive colour, then add clear frit or powder to cover the overlap area before adding the second reactive colour. The clear separates the two, but does not interfere with the transition or blending because the two colours cannot interact.

It is less easy with sheets of glass where you want to avoid a reaction line. In these cases you want to have a small but consistent gap between the reactive pieces. Place the glass with the gap and fill it with clear powder or fine frit to inhibit the reaction. You will need some experimentation to determine the necessary space between the glasses to avoid the reaction line without allowing a lot of light through, or the base glass showing as a line instead of the reaction line. After this you may decide that the reaction line is not so bad anyway!

How to make plinths for Fairs?

 Artist-led exhibitions make me realise why we pay commissions to galleries.

I spent a whole of a day making table-like plinths for the exhibition.

These are simple objects that require stability, must be plain to avoid competing with the object(s) on it, and - in our case - must be flexible and easy to store.

Based on two different design suggestions, I have constructed a table supported -but not attached - on a pair of right angle support legs. These legs are hinged so the whole can be closed and stored flat. As the legs are hinged, each pair can be combined to form a square plinth with the addition of a top.

The process of construction is simple too - although it does take time. The four I made took most of the day with the usual interruptions.

First you use a butt hinge to make the right angle supports. This is arranged so the support cannot open beyond a right angle:

When this pair of supports is screwed together, you place them on the up-turned top and place battens round the supports for security:

Finally, turn upright and paint.