Using Wet Cutting And Wet Sanding to Greatly Improve your Finish.
One of the marks of a master craftsman is how smooth he can get his finished turnings. The extremely smooth surface is a delight to see, feel and to apply finish. There are several factors that influence how smooth the final surface will be come:
Skill of the operator
Sharpness of the tool
Type of tool
Quality of the timber
By improving any of these factors the end result will improve. If you improve all of the factors the results can be quite dramatic. I was pleased to find that wet cutting and wet sanding worked so well that in some cases you can start sanding at 320 to 400 grit sandpaper if the quality of the wood is good enough.
Description Of The "Wet-Wet" Technique
The "Wet-Wet" technique involves wet cutting and wet sanding. Wet cutting technique gives superior final cuts by making very fine, shallow cuts on a wet surface. Remember that the wood is "dry wood" that has the surface "wet with something like sanding sealer, your favorite finish, or wax. A good wetting agent is a diluted sanding sealer. I am presently using Deft sanding sealer diluted 50/50 with lacquer thinner. A water based sanding sealer might work just as well and have the advantage of being safer to work with. The wetting of the wood for the final cut may do several things: 1. May cause the tool to slide over the wood easier. 2. It may support the grain that is being cut. 3. The wetness acts as a depth gauge to make sure that you make a shallow, delicate cut.
The wet sanding seems to work well for two reasons. Since you have made a very fine final cut the requirements of the sandpaper are less. This means that you do not need to use numerous layers of course sandpaper. When you wet sand with very fine sandpaper you make a "mud" of saw dust and sanding sealer. The "mud" (sanding sealer and fine saw dust) from the wet sanding fills in the small pores of the wood and takes out the extremely fine scratches left by your tool. This gives an extraordinary smooth surface.
On soft or spalted wood you might be able to start sanding at 220 to 320 grit sandpaper. On very tight grain wood you might be able to start sanding at 400 grit sandpaper. You will use less sandpaper because you are not required to use as many course grits of sandpaper. However, the small piece fine sandpaper that you do use will have to be thrown away after being used one time.
The final cut needs to be done with a very sharp tool. For this technique to work you must re-sharpen your tool when you get ready for the final cut. To make the tool slide easier you might want to rub some wax onto your tool rest. Finally wet the wood. In my case, sanding sealer diluted 50/50 with lacquer thinner. Let it soak in for about 15 seconds. Wipe the excess off with kitchen paper. Then turn the lathe on and make very light shallow cuts, with the bevel rubbing.
Description Of Project
To develop the skills of the "Wet-Wet" technique it is good to start with a small project and high quality wood. For this project I wanted a small item that required some delicate skew work that could show off the technique. I decide to a lidded box from maple. I chose bird eye’s maple because it is pretty, easy to photograph fine detail and because it is soft. Soft timber can be difficult to get a smooth cut on. I figured that if I could get a pretty good finish on maple, I could get a pretty good finish on most timbers. Cocobolo is the dark accent wood. It is easy to cut and gives a superior surface with little effort. This was my first experience turning with Cocobolo. It is a delightful wood to cut but my nasal passage ways acted as though I had been turning chili pepper.
Step by Step
True up the timber end grain between centers. Make a spigot so that the round cylinder fits into your four jaw chuck with the step of the cylinder resting on top of the jaws. This is much more stable than just holding the timber by the inside surface of the jaws. Mark off the top and bottom of the box with a pencil and start rough shaping the box. I recommend that you do your rough out with a skew. Although roughing out gouges might be faster, this will be a good skew practice. Since you will be making your final cuts with a skew, this practice at roughing out with a skew will get you "warmed up."
Turn a step spigot at the top of the box. This will allow you to later mount the top of the box to turn the inside. Rough shape the bottom of the box. Then drill out the inside of the box with a Forstner bit. Clean up the inside and bottom with a sharp scrapper. Try to make delicate fine cuts. When you have the best cut that you can get with your scrapper, wet the inside of the box with you finish. Let the finish soak in for about 15 seconds then wipe it off with kitchen paper.
Now with the dry timber still moist from the finish, make a very light finish cut on the inside of the box. Re-sharpen and hone your scrapper before using it. Do not cut all the way through the "wet" timber. If necessary repeat this step two or three times to get an extremely fine surface. Next wet the surface again with your finish and wet sand. I can normally start sanding at 320 or 400 grit sandpaper. The wet sanding create a "mud" of finish and sanding sealer which fills pours of the timber. Sand to your desired grit and apply one more coat of finish. Wipe this off with kitchen paper. The inside bottom of the box is now finished.
Now start making the final shape to the bottom of the box. When you are satisfied with the shape wet the timber with your finish. Make a very light cut with the skew. My finish stays in a glass jar that has duct tape around it so that it will not break if knocked over. I have shortened the handle of a good quality brush so that it will fit inside the jar. The brush "lives" inside the jar and is never cleaned or lost.
Sharpen your skew and make a very light cut going down hill on the bottom of the box. Again do not cut all the way through the
timber. Repeat this step several times if necessary so that you have a very smooth cut on the wet timber. The best cut you'll probably be able to get on this soft wood will allow you to start wet sanding at 320. Wet the wood again and then start sanding. You will find that Kingspore sandpaper works very well for this technique. It is a high quality sandpaper that works very well when wet or "stuffed" into a tight corner.
Next, turn a spigot at the bottom of the bowl so that it can be mounted into a base. To make sure that the bottom of the bowl fits flush with the base, undercut the bottom where it joins the tenon. Part the tenon off and set the bottom of the bowl aside for a while.
Making the Top
Now mount the timber blank for the top of the box in your four jaw chuck. Use your skew to make sure the bottom part of the top is flat. Use a straight edge to check. Glue a 1/4 inch thick of contrasting timber to the top blank. Be sure to glue end grain to end grain. If you glue cross grain accent wood to end grain body of the box, the accent piece is likely to chip out when you start turning. I used Cocobolo for a contrasting color. Hold the wood in place with your tail-stock. I used a large block of walnut to apply even pressure to the Cocobolo. When the glue has cured turn the piece true and square up the bottom.
Use your calipers to get the outside diameter of the lid spigot from the bottom of the box. Use this measurement to mark the diameter hole to cut in the top of the lid. Use a round nose scrapper to cut the dome of the lid. Use a straight scrapper to make the final cuts on the lid so that it fits snugly over the bottom of the box. Go for a nice smooth fit at this time. Wet cut and wet sand the inside of the lid.
Place the bottom onto the lid and hold it in place with the tail-stock. Shape the top of the box, being careful to blend it in smoothly with the bottom. This is where it is important that you have glued end grain to end grain. It will cut much smoother and not be as likely to chip out. Wet sand and apply finish. Cut a 9/16 inch tenon at the bottom of the box. Use an open ended wrench that you have ground a cutting edge on. This is a fast accurate way to get consistent tenons.
Finishing the Top
Make a spigot from soft wood for the top to fit on. Be sure to have a snug fit since this will be turning the top. Be careful here because you do not want to split the top of the box with too much pressure. Blend the maple and the Cocobolo together smoothly. Sand and apply finish. Wipe the finish off with kitchen paper.
Use small shallow gouges and skews to shape the top. It may be necessary to place duct tape around your spigot to give it a little more retention for turning. The new collet jaws from Oneway are ideal for this purpose. Turn the wood round with a small shallow bowl gouge. Work from the top of the finial down. In this way you are working from the small delicate part to the larger, stronger part of the finial. Sand and finish as you work you way down the finale. Cocobolo cuts so well that you can probably start sanding at 400 to 600 grit sandpaper.
Making The Base
Glue a 1 3/4 inch piece of end grain Cocobolo to a waist block that has been prepared to fit in your four jaw chuck or for your faceplate. True the base with your skew or gouge. Shape the base with your small shallow gouge and skew. Leave a central area large enough for your ½ inch spigot from the bottom of the box to fit into. Use a 1/2 inch Forstner bit to make a 1/4 inch deep hole in the base. Test fit the bottom of the box to make sure that it fits snugly to the base.
Make the top of the base around the hole concave so that the box will fit snugly to the base. Cut a pedestal 1/4 inch diameter next to the platform that supports the base. Make the pedestal narrower toward the bottom of the base. Be careful here because the pedestal is thin and weak. Sand and finish at each step. You can not go back to distant area once the pedestal becomes thin or narrow. When you are satisfied with the fit, part the base off with a thin parting tool. If you do a careful job of parting off the base light sanding will be sufficient for the base and reverse turning is not necessary.
Now glue the box to the base with CA glue. Be careful to wipe up any excess.
Apply the finish of your choice, I use the Beal buffing system. Buffed very lightly with Carnuba wax for about 60 seconds. The Beal is a very quick and nice buffing system if you like a satin finish.