Duplicator

[jklett]

I attempted to make a duplicator similar to yours and I am having a big problem with tearout. I know it is the grind on the bit because I tried the same bit in the tool holder with the same results(it's an older logan metal lathe). I tried different types of wood and it tears everything, even maple which I had the best finishes with in the past. I've turned wood on this machine before, but I can't find the bit I used and I can't remember how I ground the bit to have it work right in the first place. What's the trick to this? I tried a square bit ground to a 60 deg. point with the nose radiused slightly, a thread cutting bit, and a radiused 90 deg. bit. I tried cutting on center, above center, and below all to no avail except above seemed to be the smoothest although I could only cut .020" at a pass and this machine can do brass at that depth. I even played around with the top and side angles and not much difference. Can you suggest anything for me to try? I know it shouldn't tear the wood up this much and I'm about at my wit's end with this.

[capesams]

I have found the half round works the best of all the different cutter's....tool steel.

[ProfessorM]

I agree with Capesam that a radius bit is the best. I use a 60 degree bit too. I like a much smaller radius on the point than Capesams. I find that if I use a big radius on the tip I get a little vibration, especially if I am doing a small dia. plug or a hard material like rock maple into a needle. I too use high speed steel, 1/2 square, but also use carbid ground the same way. I add an angle on the bit, if you look at the front view, that I think makes the tool cut much cleaner. The side view, like CS's, has the much needed angle also. I have never experienced any tearout but with a sharp point the finish looks like crap which is why you need the radius on the point. Maybe you are being too aggressive with the amout of stock you are trying to remove . Maybe your RPM's are too slow but you said you did it before. Try what Capesam's and I suggested and if still can't get good results send me the bit and I will grind for you. Paul

[capesams]

my cutter is only 5/16 x 5/16 th's..I tried the same point as you have showing in your pic..but still got tear out.....and I move like a snail using my dupy...the half round has worked the best for me so far......also if you take your stock and rough it out round with your chisel first close to what dia. your looking for , then use your dupy to finish, it will keep your cutting head sharper longer.

pitch in the wood will dull even carbide after a bit.

[ProfessorM]

Capesams did you also put the angle on the front too. Not the relief angle on the front top to bottom but the angle side to side on the front picture. I found if you leave the tool flat on the top it will not finish as good. The half round was the tool I first started out with but switched to the type I am using now with no problems and I seem to be able to go faster. You will definitely get a smoother finish with a larger radius, but I think you can go faster with a sharper point. Trying to get best of both worlds. I don't know maybe I am just getting lucky. I am by no means an expert in wood turning. I just use what I know about metal and hope it apply's somewhat into wood too. You really do need to stone the tool to keep a sharp edge. I too move at a slow pace, especially after I launched that needle thing into my forehead. Gun shy now. You are right on about roughing stock round it will definitely help out in saving the tool edge life. Paul

[Slipknot]

You guys rock

[capesams]

Karl...told ya it would be a wood eater ..good show.

Paul..I bevel the cutting edge[sides] all the way around.....after a touch up on the stone....she throws lots of curly shaving's......but if I try to take off to much at once she just digs in and take's a big bite out of the wood////to sharp maybe.

[ProfessorM]

I found in my limited wood turning with the dup. that if you get too aggressive and try to take off too much that it will grab and dig in and tear. I think it is hard to take tool away from stock quick enough once you make the mistake of being too agressive. You seem to have much more control of a single wood turning tool than the control of the dup. cutter. It being larger and heavier than a single tool, which is what you need, sometimes cause's me to be too aggressive and I can't correct it fast enough so not to dig in and sometimes rip piece out. There is a fine line between the two but practice makes perfect. You want the dup. tool holder to move smoothly and effortlessly across the base but it also can cause you to slide too far in and then you get the big bite at once problem. There is definitely a touch to it. Tool being too sharp will cause the tool to have no resistence when applied to the stock so it just digs in like butter to wood which is soft as far as materials go and if you are not quick enough to pull tool away than you get the big bite, thus the touch. It is only a split second. I know in maching brass and even titianium in some operations, drilling esp., that we always dull the cutting edge of the tool so it does not grab. I still think you want a sharp edge though in wood. Just my 2 cents. Paul;