Hey All, I just started cutting circular blanks on my bandsaw and I want to know if there is a table, or guide that indicates the minimum radius that can be cut depending on the width of the blade(regardless of the blade width).
Thanks in advance for your suggestions. Marc
"marc rosen" wrote: (clip) the minimum radius that can be cut depending on the width of the blade (clip) ^^^^^^^^^^^^^^^^ It actually depends on the ratio of the width of the blade to the width of the kerf, which in turn depends on the tooth set. Furthermore, you can force a tighter radius by doing a little back and fill motion as your cut progresses.
Marc, I have some cardboard disks cut out at 1" diameter intervals. I lay the biggest that will fit on top of the blank, mark it somehow, and free-hand cut the pen blanks off ;-)
Mathematically, what you are looking at is the answer to the question of how much blade at what tangent will fit between two circles (the scrap and the keeper stock describe two circles ABOUT 1/8" apart.)
If you care to do that math, fine. But I see no reason to bother unless you are planning on cutting a couple hundred all the same and are looking to find the "one perfect blade" to make that cut. I, however, cut one at a time and seldom cut two in a row the same size. Changing to the ideal blade for each piece is just too much of a hassle with too little payback.
Frankly, I just make the cut as directly as I can. If the blade is struggling to make the turn, I widen the kerf and have another go at it. I might even straighten out the cut and remove that piece of scrap altogether, then begin the cut anew.
Normally I then take two of the best looking arcs as support for a center-finder head and mark the APPROXIMATE center. If I take a third or
4th line, there is never exact agreement because I haven't actually cut a perfect circle. But two lines make an intersection that is close enough for the next step in the process.Bill
Perhaps not quite as precise as other answers, but this might help.
Try this link.
(watch the wrap)
BillR
Hey Guys, Thanks for the links and the advice. Yeah, I was getting too analytical but the tables look helpful if I want to grab a specific blade to cut out a single. or a series of blanks. I don't have a cutting jig yet but I am building a circle cutting jig based on some magazine plans.
I've got a new topic which I'll post momentarilly. Thanks again, Marc
I use the same method as Bill, I have cardboard discs each slightl
bigger. Mark using the biggest and cut parts at a time as the turn o the blade will let me. Also i have a small hole cut in the center of each cardboard disc whic i also mark thus straight off the bandsaw,on with the face plate an tidy up the outside of the blank on the lathe. Mar
Hello Marc,
There are tables that give the info you need. I am sure they are in the Machinist Handbook, but alas, it is at home right now. Some blades have the info on the back of the package they come in. Note that I purchase an 82" 1/4 inch blade and use it for all my cutting. I have a Jet 1236 so my swing is somehat less than the big boys.
The procedure I use is as follows:
The log is cut with a rip chain on my chainsaw with the pith being removed. This results in 3 or 4 flat pieces (usually). Sometimes I let them dry for few months, other times I turn green. I take the flat piece and with a compass mark out the diameter I want. I make sure the center point is well marked as well as the diamter. The piece is then taken to my bandsaw and sawn. This oft times results in a fairly good round piece. The rounded piece is then either turned between centers or attached to a faceplate. Swapping out blades for different cuts would be a bit of a time waster for me as all my bowls are well within the tolerance of my lathe's swing and the type of turning I do. The only real bit of 'accuracy' I strive for is on the tennon as the Nova chuck I use is rather limited in its spread (approx. 1.75 to 2.00). I have the midi Cole jaws attached to my other Nova chuck for finishing the bottom.
Bill's suggestion to use cardboard cutouts is a really good one. One minor improvement may be to make the cardboard cutouts out of some stiffer more durable material and have a hole in the center of the cutouts. The center on the blank can then be marked without not much effort.
I'm sure I cribbed that idea from someone. I do have a hole in the middle where I tap a nail to mark the center (if I remember to do it).
But the circle I cut isn't going to be especially round, so, whether I mark the center before or after cutting, it's still gonna carry a fudge factor with it.
Now Darrell Feltmate ... now there's the man! He says (IIRC) that he printed concentric circles on a sheet of acetate and can not only select for size, but also for grain presentation. Seems to me that if you then punch a hole in the acetate film to mark the center and let the tip of a crayon pass through to mark the circumference, you'd be in pig heaven!
Once you get out past 8" diameter, though, I think you'll need to either chum up with someone who has a large format printer or a stack of cardboard circles. Then, too, there's no law against notching a stick every inch or so, starting with a nail to use as a center pin.
Bill
InspirePoint website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.