Mounting Wood On The Lathe
Collated from newsgroup postings.
I am still shopping around for a chuck, and in the meantime have tried alternative methods of mounting. one thing I tried is gluing it to a waste block with medium consistency CA glue and then I let it cure overnight. I put it up on my lathe and started turning away. before I knew it, it broke right off. I took care to sand both blocks down. it was a blank about 4x2 so it wasn't very large, and I glued almost its entire surface to the waste block. I'm pretty sure it wasn't the wood that caused the problem. they were both perfectly seasoned hardwoods. can somebody please tell me what I did wrong?
- Try polyurethane glue. Dampen one surface first, as it is water-catalyzed. When cured, this stuff is scary- strong. It also cuts easily without traumatising your tools. (I've never had much luck getting CA to hold up in any sort of shock-load situation. Save the CA for infilling cracks with sawdust!)
- Even lowly woodworking glue will form a bond stronger than the surrounding wood. However, the dried excess will dull your tools quickly.
- Recess the centre of the waste block by a little bit so that the glue joint is only around the outside 1" or so. If either the workpiece or the waste block have any convexness at all and there's no recess, you will have a good joint only at the very centre, and a compromised joint all around the perimeter, where you need it the most.
Assuming that "block" means square edges;
- To much speed
- Too heavy cut at first
- Too much CA
- Did you put small amount of pressure on it first minute of set time?
- Using roughing gouge and tip of tool too low, top side edge of tool caught on sharp edge of block?
- Type of wood, very hard therefore no CA when into pores to help hold.
- Too soft wood and too much CA was absorbed not leaving enough between pieces.
- CA glue too old, also sunlight will cause it to go bad in the bottle.
While roughing out, as soon as the tool engages the wood, I no longer look at the point where the tool is contacting, instead, I shift my eyes and look at the top of the block. This allows me to see the depth of cut I am making as I traverse the tool across the block. Also, when using a roughing gouge, if going left to right, I move the back of the handle slightly to my left, this ensures the top edge of the tool will not hit the block edge. Move it slightly to the right when going in opposite direction. (this is just my way of handling it, there isn't a right or wrong way)
If you were using a roughing gouge and think this may have been the problem, on a block that small you could switch to a spindle gouge for roughing and see if you have the same problem. There are probably many more possibilities.
CA glue needs a close fit to work effectively. I would use yellow carpenter's glue, you can use a sheet of paper between the blocks, to make it easier to separate. Or no paper, which is what I do, I'll just reach around with a thin parting tool and cut a concave bottom to part it off just ahead of the glue joint. Then finish it up with a 2 in. velcro disk chucked in a drill.
If you are set on using CA, go ahead, then after you think it's set, try knocking it apart. If it separates, glue it again, the first gluing will act as a primer/sealer, and the second time it should hold a lot better. You might try an application of CA on both surfaces, letting them dry, then gluing them together with a second application.
I have watched professional turners do demos at a local craft fair for years...they used CA almost exclusively with a waste block screwed to a face plate
Prepare a piece with flat bottom,spread CA (medium) on bowl blank,spray waste block with accelerator,press together and bring up tailstock and keep it there until roughing is done and glue has set....(usually only a minute or so with accelerator)....they very seldom have a piece come loose......
But I also know another guy who swears by hot glue used the same way!
The simplest, and generally strongest, method is to screw it directly to the faceplate. After the bowl is turned, it is reversed turned and the screw holes turned away, leaving the foot inside the screw hole diameter, and losing minimal thickness of the bowl.
There are bowl blanks which have very little 'spare' wood...and for a small blank, screws are a bit of overkill. I do a lot of work with limb crotches and smaller pieces of exotics where I'd be hard put to find anyplace to put screws. It's a good thing there are various options that people have developed.
Glue blocks, chucks etc. are all perfectly good ways to mount pieces. I was trying to point out that sometimes it gets more complicated than it needs to be, particularly for people starting out.
I get all my wood for free so I'm not so concerned about separate waste blocks. I just screw a whole blank to the face plate and turn away... both inside and out making sure to allow for the faceplate screw clearance when shaping and finally parting off. The left over chunk on the faceplate is removed and burned in the woodstove, no waste.
There are many ways of doing this that will work. I've had success using double sided tape to attach wood to a faceplate. I clamp it overnight before I start turning. I've also glued wood to a scrap block using carpenters glue. Sometimes I'll turn the wood between centres first and leave a spigot at one end, then I'll turn a recess into the scrap block to accept the spigot. This greatly increases the holding power.
Since you are allowing the CA to dry over night why not use yellow glue? When it dries I believe there is nothing that will separate the joint short of the wood itself giving way A very strong bond and a lot cheaper than CA glue.
A simple solution that I used for a couple of years and for that matter still use today.
- Mount the blank to a face plate and turn the outside of the bowl.
- Flatten the bottom. Hot glue a wood block to the bottom of the bowl and bring up the tail stock as a clamp for a minute to let the glue cool.
- Turn the block to the outer diameter of your face plate.
- Remove the bowl from the lathe, take the face plate from the top and mount it to the block on the bottom, remount and turn.
Works great. When done just use a parting tool on the glue line until about a one inch tenon is left and the heat of the parting cut will allow you to remove the bowl and proceed to finish the bottom.
It might be good idea at this point for anyone who has never used hot glue to point out that there is a special hot glue stick made for "wood" use. The one's I've seen are yellow. I wouldn't recommend using the fabric sticks that generally come with a glue gun kit for this purpose.
Back to the Articles page