Tips & Techniques

At the bottom of these pictures you may find text that elaborates on a particular picture

26jan07 Dial Glass Grinding. For radios with missing round, convex Dial Glass covers you can buy new covers from Bill Turner in Missouri. If he hasn't got exactly the diameter you need, just order one a quarter inch to a half inch larger and grind it down as shown above. Masking tape both sides to help prevent cracking during the grinding and to help protect your fingers if the glass does crack. Also the tape allows you to use wood glue to attach the perfect circle paper template to the tape. I started with 120 grit paper but it soon wore out and I changed it for coarser 80 grit paper. This grinding wore out three new sheets of paper to take off 1/4 inch all around circumference of this glass. Don't push the glass too hard against the belt or you will build up too much heat in one spot and that may crack the glass. Rotate it evenly. Grind one rotation on the front edge then turn the glass around (left to right) and grind another complete rotation on the back side. Don't hold the glass plumb to the belt. Angle it about 15 degrees to the belt. It will take about 25 minutes to grind off about 1/4 inch from all around a 4 inch diameter dial glass. <<< end >>>

17feb07 Colouring and using 2-Part epoxy for radio restoration. by Don Tutt (This article published in Jan07 issue of Oklahoma Vintage Radio Collectors "Broadcast News" newsletter.... google them) See pictures above.

I use 2-part epoxy glue in my wood and bakelite radio restoration work. It is versatile, strong and easy to use. I recently dealt with a 1935 RCA floor radio's wooden cabinet where I had two long, narrow (3/32"), vertical grooves to fill. They were each between two adjacent and different veneers. I wanted a filler that would bind the underlying wood together and make a smooth, dark brown transition between the veneers. I hoped to not totally fill the gap in order to get the appearance of a shallow groove. The task was made more complicated because the gaps were at the left and right front corners and went almost the full length from floor to top of the cabinet. The technique required the cabinet to be set on its side and tilted until the gap line is both level and oriented so a liquid poured into the gap will flow equally up each side of the gap. This technique is akin to pouring an epoxy fillet into a 90 degree corner in order to strengthen the corner. You set the corner up so the epoxy fillet sets solid at 45 degrees.

My materials list is:
1. a big bucket of patience....
2. I use G2, a 2-part epoxy made by Industrial Formulators.
3. Epoxy Paste Pigments
4. several 4 inch square pieces of wax paper
5. about six 3-inch spikes
6. a heat gun
7. a "discarded" muffin tin from the kitchen
8. a small slot screw driver
9. an old 35 mm film canister and
10. a little plastic 1 oz Dixie cup about the same size as the film canister.

The G2, 2-part epoxy is made by Industrial Formulators, (google G2 Epoxy Wood Glue, and you'll find it) At room temperature 70* F. it has an 8 hour open time. After mixing 2:1 (2 parts Resin, 1 part Hardener) I coloured the epoxy dark brown using Epoxy Paste Pigment made by System Three Resins Inc. Ste. 105, 3500 West Valley Hwy North, Auburn WA 98001. They pack it in 4 oz plastic jars. TIP: When opening a new pigment jar I prevent the pigment from getting all over everything on the work bench by immediately and completely cleaning the underside of the lid and the jar rim and threads with a succession of small rags moistened with lacquer thinner. Totally clean, no gooey bits anywhere. After that the jar NEVER gets tipped over. With this stuff it pays to be anal about clean. Otherwise you'll be wearing lots of pigment on your work bench, tool handles and fingers and it takes a while to wear off. Avoid getting the thinner in the pigment.

Assuming you can't buy ready made brown pigment you'll have to mix your own. Mixing the epoxy paste pigment is an art and is the first step. Brown is tricky because it is made up of at least three colours: yellow, red and black. (You can get away with only red and black.) The approximate proportions by volume are... 8 yellow, 3.5 red, 1 or less for black. Use a spike to dip into the yellow pigment and come out with a blob the size of a green pea. Put 8 of these blobs into the film canister. Use a different spike to add a bit less than half, 3.5 blobs, of red pigment. Set the yellow and red spikes apart on wax paper. Take a new spike and thoroughly stir the two pigments together to get a reddish mix as the outcome.

With the following test you want to find out how to adjust the balance between the yellow and red. Place a small test blob of your reddish mix on a 4" by 4" piece of wax paper. Dip a very tiny bit of black pigment onto the tip of another spike and deposit this ink beside the reddish test blob. Set the black spike aside. With yet another clean spike gradually stir the black into the reddish test blob. If you have the ratio of yellow and red correct you will get a nice shade of brown. You'll get blackish brown if you add too much black.

Assuming the bit of black is added and you are not happy with the "brown" try adding a tiny bit of yellow to see if that is the direction you need to go in. If this browns up your test blob then you know you need to add more yellow to your main mix BEFORE you start adding black to it. If the yellow didn't move your test blob toward the brown colour you want, then you need to add some red. So, deposit another same-sized fresh test blob of your main reddish mix on wax paper, stir in the same small amount of black and then lay a little pure red pigment beside it. Stir in a little red at a time to see the effect. If you get the brown you want you then know your main batch needs more red BEFORE you start adding black to it. On the basis of how much correction you do to your test blob you estimate how much more red or yellow to add to your main batch. Add that and mix it in well. Carefully add the black, drop at a time until you get a nice medium-to-light brown. Don't go too dark yet. You have just made your little supply of brown "mother sauce" for present and future use. It will colour a fair bit of epoxy resin glue.

Now mix enough G2 resin and hardener to fill the one gap (not both!). Use one of the clean, degreased metal cups in the muffin tin. Now add some brown "mother sauce" pigment. Don't overload the G2 resin with colouring or it won't set. If you have, say, two tablespoons of mixed resin use the volume of a garden pea as the amount of pigment to add. Note the G2 resin picks up the brown pigment colour without seeming to alter the brown colour too much. Now, carefully stir in very small amounts of black pigment until you get the deeper brown that you want for this job.

Take a 3/32" drill bit and drill three holes close together and one above the other, on the side of the Dixie cup. Start the first hole at the bottom of the cup, but on the side. Add the other two holes above it.

Use the heat gun to warm the brown epoxy glue in the muffin tin. I use the metal muffin tin because plastic Dixie cups melt with such heat. Play the heat under the cup and also right at the surface of the resin. You'll notice the air bubbles coming out of the resin. Get the resin very, very warm but not boiling hot. You'll see its viscosity gets really thin. Heating the resin will drastically reduce the open time from 8 hours to about 1 hour which is plenty for this task.

Now you need to work quickly and accurately because the heated epoxy stays "thin" for a minute or two and it won't dribble out the three holes nicely unless it is hot and thin. Pour the hot epoxy into the Dixie cup with the holes. Hold the cup in such a way that the holes are up and no glue comes out. Move over to your cabinet, get above the gap and rotate the Dixie cup so the holes are down. Watch for the thin dribble of glue to start dropping toward the gap. Move along as required, supporting your shaky hand on the radio cabinet. Don't stop pouring. AFTER doing the whole pour end to end, clean any sideways spills with a paper towel wetted with a bit of lacquer thinner .

You won't get a really even pour. There will be slightly high and low sections. You may have to do a second "pour" later. For now, fix what you can by carefully warming the glue in the gap using the heat gun on its low setting. You don't want to burn the veneer, move the gun around. The epoxy viscosity will thin again and you'll see it flow into the low places. You may have to use a small slot screw driver to add a little more epoxy here and there or to scrape out a bit of excess. Do a final tidy up with the paper towel, lightly moistened with lacquer thinner.

If you are worried about the coloured epoxy staining adjacent veneer then you might consider first giving the veneer around the gap a spray coating of lacquer sanding sealer. I didn't and cleaning up "spills" seemed to work fine, with no adverse staining.

Leave overnight, it'll set to a glossy finish. When all gaps are filled you may wish to sand this epoxy to the final contour you want and then when you start spraying your lacquer finish the dulled surface of the sanded brown epoxy will gloss up nicely to blend in with surrounding luster of the adjacent veneer.

TIP: Store any left over mixed epoxy resin in the freezer for use in tomorrow's glue up. If you haven't heated it it should keep several days. If, as in this case you did super-heat it you may get another use out of it the next day. In cold weather it is good to heat the resin a little bit to kick start the molecular bonding that leads to the resin hardening. Sometimes I will come into the shop the next morning and find the epoxy has not set. The shop was too cool. My error.

Coincidently, that left over brown "mother sauce" can be used to colour the same G2 epoxy for use in making your own "plastic" knobs..... but that's another story, for later.

To find out which primary colours are needed to mix other colours try using your computer's drawing software. Draw a box or circle, select the fill tool to assign the box a colour. The fill tool may display a breakdown of the CYMK (C = Cyan, a blue colour, Y = Yellow, M = Magenta, a reddish colour, K = blacK) colours used to make the fill colour for the box. Doing this I found that the shade of brown I had chosen was comprised of 20 Yellow, 20 Magenta and 60 blacK. Those proportions are a trap for us in that they apply to the colour standard of your computer monitor and NOT for inks or pigments that we use. The only useful thing is the basic knowledge that yellow, red and black comprise brown. You'll note I corrected the proportions above.

Consulting a (PCFG) Pantone Colour Formula Guide booklet will show you the many shades and hues of hundreds of colours and the proportions of basic colours that make them up. The print industry's pressmen use these to guide them in mixing the press inks for spot colours. From the Pantone Guide you would learn that the various browns are made up of various combinations of Cyan (blue), Yellow, Magenta (red) and blacK. I keep it simple and use the draw package to get a hint as to where to start. Then I play. This works fine for wood cabinet repair but you may want to get a lot fussier in your effort to match your bakelite or plastic colours. If so buy the PCF Guide and go from there. Be careful there are several different colour guides used in the print business. Insist on the PCFG. Your local printer might help you find one or have a used (slightly faded) one he will sell you cheap so he can use the money towards a new one for around 100 bucks. Graphics supply stores should carry them if you want new.

TIP: For tubes with loose glass envelopes I degrease and clean the contact area with lacquer thinner on a rag, place a ring of uncoloured G2 epoxy on the glass as close to the tube base as possible. Use a heat gun to flow the resin down into the tube base. Wipe of the excess with a lacquer wetted paper towel. Stand tube upright in a "holder" overnight.
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As time allows this section will be expanded to include tips or descriptions of techniques in the areas listed below. Meanwhile you can find some tips on these subjects elsewhere in this site.

chassis overhaul + wood cabinet repair + wood cabinet refinishing using Mohawk products + plastic or bakelite cabinet repairs and refinishing