sanding turned wood on the lathe

[skeetstar]

gentles all, I am a relativity new turner, mostly with hardwood. I turned something the other day, softwood that I thought was well seasoned. After finishing with wax, the next day some micro cracks started to appear.. more apparent to touch than sight. The cracks followed the grain so weren't unusual in that respect.

Question

When I sand, I tend to sand at high revs, and also exert plenty of pressure. This means I usually have to fold the paper into multi layers and ensure that I don't keep sanding for too long without a break cos the things get a bit hot.

The wood never gets very hot, but does get warm, could the crack be as a result of my sanding technique?
Should I be sanding a bit lighter but for longer?

 

[Tris]

Go through grades from, say 120g, through to 400, maybe 600 for a very close grained timber. Don't let heat build up, if it feels hot to touch it's probably too hot.
Sometimes you can get cracking from a release of stresses in the timber when it is cut, but I think it's more likely heat

 

[Phil Pascoe]

Slow it right down, use a good quality abrasive and a light touch. Practice your techniques until you very rarely need anything coarser than 120g.

 

[Steliz]

I think it's a matter of working it out for yourself. I try to get as close as I can to a finished surface with the tools before sanding. If I press too hard with the sandpaper it gets too hot but if I press lightly then the sanding takes longer.

 

[Stigmorgan]

Slow speed and light pressure, the harder you press the deeper the scratches will be therefore you will have to do more sanding, also at higher speeds and harder pressure the sand paper will deteriorate at a much faster rate, I learned this all the hard way too, also I rarely use sandpaper any more, look into sanding mesh, it lasts longer and doesn't leave grit on the workpiece.

 

[Richard_C]

As others have said, slow and only modest pressure but be sure to keep the abrasive moving side to side so it doesn't create new lines. Some woods react really badly to heat. When I started out, sanding took a lot longer than turning with the tools. As you get better the finish off the tool gets better and you do a lot less sanding. I am not that experienced but often now it's just a quick, 20 or 30 second, application of 120 grit then up through the grades.

 

[Andy's Shed]

As a new Woodturner myself I'm finding this thread very helpful, tool marks are a problem for me at the moment.

 

[Robbo3]

Sanding on the lathe is normally done at 500 RPM or less.
Let the abrasive do the work by using light pressure & keeping it on the move.
Don't be afraid to start with 60 grit, or even 40, if that is what is needed. No one but you is going to know.
Work your way up through the grits but don't jump more than 100/120 each time.

 

[Fergie 307]

I find an old leather belt is useful. Just stick the paper to it then you can easily move it up and down the work. Also use old car timing belts, free at any garage.

 

[leisurefix]

Yew will develop micro cracks from heat far too easily, so you have to be really careful when sanding it.
Great advice from Robbo3, start with whatever grit you need, rather than spending ages with a fine grit.

 

[scockram]

I often reverse the direction of rotation, (between centre mounted work), for sanding, when I remember. I've got the idea that it helps, maybe heard it somewhere but can't remember now, but no proof.
Anyone else do this or heard of it?

 

[Phil Pascoe]

Yes, it does, because you get the bits that are against the grain but most lathes don't run in reverse and besides you need a chuck that you can lock to the spindle or it'll spin off. Visualise planing a piece of wood against the grain.

 

[Robbo3]

Just to clarify the point, if you run the lathe in reverse with the wood mounted in the chuck & the chuck doesn't have a means of locking it to the headstock, then it may unthread itself. If the wood is mounted in a chuck & supported by the tailstock centre, then the chuck can't unscrew. If you use a drive centre held in the chuck, then effectively the wood is mounted between centres & you can run the lathe in reverse.

 

[skeetstar]

Thanks all, in the past I've got good results by going 80, 120, 180 then 240 grit.. but that was all on hardwood. I'll change rechnique, use lower revs and less pressure. Some really good advice here, this really is a great forum. I've got a Yew log that I will start to use next year, I'll make sure that is sanded very gently per leisurefix's advice.

Again thanks for all the input, much appreciated.

 

[Richard_C]

And just to add, there are times when odd recalcitrant tool marks across the end grain sections just won't sand out with the lathe running. Stop the lathe and hand sand along the grain, across the marks. Takes effort and time but sometimes the only way. You can finish off lathe running with the finer grades.

 

[Richard_C]

I've got a Yew log that I will start to use next year

Yew is one of my favourites, botanically a softwood but behaves and polishes like hardwood. Some people, including me, are sensitive to the dust from yew sanding - if I don't take proper precautions I end up coughing and spluttering later in the day. Enjoy using it but make sure you wear a dust mask even for a 30 second sand, and do what you can to minimise breathing it in.

 

[Fergie 307]

A tip I was shown years ago for gunstocks is to get it nice and smooth, then dampen the surface and go over it again with about 400 grit wet and dry. The idea is the fibres swell slightly when dampened, you rub off the surface, then it dries and the fibres shrink back leaving it as smooth as the proverbial baby's behind. Works really well if you are looking for a super smooth finish.

 

[Phil Pascoe]

Steam is better (quicker) for small items. It works well for lifting small dents as well, and is worth a go before using sanding sealer I've had finishes go patchy with s/s, there's no danger with water.

 

[scockram]

Just to clarify the point, if you run the lathe in reverse with the wood mounted in the chuck & the chuck doesn't have a means of locking it to the headstock, then it may unthread itself. If the wood is mounted in a chuck & supported by the tailstock centre, then the chuck can't unscrew. If you use a drive centre held in the chuck, then effectively the wood is mounted between centres & you can run the lathe in reverse.

Looks like I might have been a bit ambiguous with my post. I only run in reverse when the workpiece is mounted between centres. I don't have a locking chuck, and besides, don't use it very often anyway. It'll treat myself to a new and better one sometime.

My dad smashed his face up years ago when a piece of wood came out of the lathe. There wasn't much in the way of PPE in those days, so following that he made himself up a protective face shield from a motorcycle helmet somehow.

 

[Robbo3]

No, you were correct. You clearly stated with wood between centres.