What Causes This?
- Thread starter renowb
- Start date
Signed-In Members Don't See This Ad
Signed-In Members Don't See This Ad
Rhys_holland
Member
looks like your holding a skew flat against the pen blank try using a different tool
Isn't that a weird thing? I've had that happen to a couple TrueStone blanks I was working. Both the gouge and skew. No matter what I tried....changing the speed or changing my cutting style, I couldn't get rid of it. I ended up using a 60 grit sandpaper to smooth things out and then continued turning.
arioux
Member
Have you tried just one blank at the time on the mandrel?
Yes, it does it when I do a Sierra blank, too. I have tried speed changes, too. Sharp tools also. I also go with the sandpaper to smooth it out. Dunno.
wood8ug
Member
Looks like chatter or bounce. new to turning so i've seen this when the material that is being turned vibrates or flexes back from the turning tool and is not cutting symmetrically it can cause a chatter?
steve
steve
workinforwood
Member
I don't even know what it is I'm looking at, other than the obvious pen blanks on a mandrel, so I can't guess the problems.
thewishman
Member
I've had that happen. My tools were not as sharp as they needed to be.
If it was uniform, you could claim a higher price for the special texture.:wink:
If it was uniform, you could claim a higher price for the special texture.:wink:
pensbydesign
Member
had this happen today with apiece of cross cut ebony, sharpened my skew and took lighter cuts, eliminated 98% of the chatter. i did clean up the rest by using the skew as a scraper, holding it level flat on its side taking very light cuts. light cuts and sharp tools i think is key.
ed4copies
Local Chapter Manager
Donna
Member
Are your headstock and tailstock out of alignment?
PenMan1
Member
It looks like too much tool pressure to me. When a tools starts getting dull, you subconciously "push" the tool into the work causing mandrel flex.
Either that or the lathe is out of alignment.
Either that or the lathe is out of alignment.
PenMan1
Member
Try turning you lathe on its slowest speed with the tailstock out of the way. Sight down the mandrel from the tailstock end, and I bet you'll see serious "wobble".
greggas
Member
Looks like dull tool, perhaps a bent mandrel or a combination of both. Or you are fooling with us and used a Beal
Hillbilly
Member
I've never seen it either. I have messed up a lot of blanks and made all the mistakes, this is the first for me. I thought the same as Ed I thought I was looking at alt casin. What kind of blank is it? I cant see how you could do that without having a obvious vibration.
soligen
Member
I've has this happen when using a scraper - makes a screach noise too. Its vibration and once the hills and valleys form, its hard to get rid of them.
I dont get this with a skew and planing cut - just scraper action, and yes, even a carbde has done it. The less stiffness, the more likely. Take very light cuts and be sure your tool is very sharp is the best advice, but I havent figured out a sure fire way to avoid it except avoid the scraper. I've had it happen on a fresh carbide insert, so sharpness is not the only factor. What I do lately is a planing cut with the skew to get me close, then just the scraper at the end for smooth final passes becasue I''m not good enough with the skew yet (at least this way I get some skew practice)
I dont get this with a skew and planing cut - just scraper action, and yes, even a carbde has done it. The less stiffness, the more likely. Take very light cuts and be sure your tool is very sharp is the best advice, but I havent figured out a sure fire way to avoid it except avoid the scraper. I've had it happen on a fresh carbide insert, so sharpness is not the only factor. What I do lately is a planing cut with the skew to get me close, then just the scraper at the end for smooth final passes becasue I''m not good enough with the skew yet (at least this way I get some skew practice)
Laurenr
Member
I had that problem soon after I had purchased a used lathe, (my first). It nearly drove me crazy trying to figure it out. I called Jet, and upon their advice I replaced both sets of bearings in the headstock. Problem solved immediately.
If you lightly rest a tool somewhere on a smooth spot on the headstock, and it bounces a bit? ...then that's your problem.
If you lightly rest a tool somewhere on a smooth spot on the headstock, and it bounces a bit? ...then that's your problem.
soligen
Member
Lauren, thats a very interesting story for this problem. If the issue for you was the headstock bearings, then I am guessing that the live center bearings could be equally probable. I have a 60deg and a mandrel saver, but I cant recall if its happened using both. Been 3 or 4 months since I used the mandrel.
My lathe was new in Aug, so I wouldn't think the bearings are going already
My lathe was new in Aug, so I wouldn't think the bearings are going already
ldb2000
Member
You answered your own question , it is chatter . Either you are using the wrong tool or using the tool wrong or your tool rest is too far away from your work piece . It is caused by an harmonic vibration between the tool and the work piece . Using a skew flat on the tool rest can cause this , especially it the skew is not sharp enough or using a thin scraper and having the tool rest is too far away from work as well . Once this chatter is started the only way to stop it is to sand it away and then go back to turning with a different tool or if it was caused by scraping with a skew then change the way you are using the skew .
If you are pushing hard with your tool the mandrel could be flexing at that end causing or contributing to the chatter. Try turning one blank at a time and see if it still happens. Also, if your tool rest is to far away from the work piece you can get a little flex in it when applying pressure as well.
jttheclockman
Member
Don't forget when turning material such as this there are both soft spots and hard spots and it will cut differently and you need to adjust your cutting procedures to accomindate. It is the same thing as with sanding grain in wood.
cschimmel
Member
I know this is probably an alignment problem. Have you experienced turners ever seen this before? It does not do it as bad on the blank by the headstock. Must be some kind of "whip" in the shaft? I went to the mandrel saver and still does not fix it.
Thanks for asking this. I have been trying to figure out why this happens sometimes and all of this great info these guys have given is such great help. Thanks to everyone that gave an answer.
jskeen
Member
I've never seen a chatter pattern that uniform along the length of a workpiece, but I'm almost sure that's what it is. To get rid of it on this piece try just putting the tube between centers and at max speed put your skew onto the blank so that NO cutting is taking place, only the blank hitting the bevel of the blade with the cutting edge of the tool at about a 20 or 30 degree angle from vertical on the blank, then very slowly raise the butt of your skew till you start getting the first fine wisps of material removed. move back and forth till the blank is smooth, and then reassemble and turn as usual.
Remember a skew used as a scraper is only half as efficient as a real scraper because of the way the edge is ground. If the bevel is evenly ground, the edge is effectively only supported by half the thickness of the tool. If you want to scrape with the flat of the tool laying flat on the toolrest, consider regrinding a skew from a > shape to a 7 shape. That way the full thickness of the tool supports the cutting edge. To be really efficient with this tool you will need to learn how to burnish a curl onto the cutting edge, but that's a different woodworking show altogether.
Good luck,
James
Remember a skew used as a scraper is only half as efficient as a real scraper because of the way the edge is ground. If the bevel is evenly ground, the edge is effectively only supported by half the thickness of the tool. If you want to scrape with the flat of the tool laying flat on the toolrest, consider regrinding a skew from a > shape to a 7 shape. That way the full thickness of the tool supports the cutting edge. To be really efficient with this tool you will need to learn how to burnish a curl onto the cutting edge, but that's a different woodworking show altogether.
Good luck,
James