We recently ran two jobs on our CNC router that turned into a large pile of wasted material... We are cutting .75" 2 sided white melamine (flake core). We cut with a Thermwood C50 - Twin 15hp spindles. We traditionally use a down spiral 1/2" bit , 18,000 at the spindle with feed rates between 300 and 600 IPM.
Twice now we used a resharpened bit and got major chipping after the second or third sheet. First bit was a compression, second a down spiral. Chipping occurs at the face (we do not cut through). In both cases, the bits were brand "new" from sharpening. First and second sheets cut well, then major chipping starts occurring (same feed rates, collection etc.)
I don't suppose it could be a spindle runout problem, since it would happen immediately. Bit does not seem to overheat (can be touched right after machining). Collets are clean, as well as shanks. I'm starting to think our supplier does not do that nice a job sharpening those bits. Any thoughts?
From contributor T:
I have not yet had cutters sharpened for our CNC. I was recently discussing this with a fellow at Onsrud. He indicated to me that when they resharpen a cutter, the relief of the cutter changes even on the first resharpen and that we won't get the same performance (cut quality and longevity) from the cutter that we will from a new one. So far, I've chosen not to go that route...
The length of time a sharpened tool should last is certainly longer than the few sheets that you mention. There are some factors that may be contributing to the short life that you are seeing. First, and probably the most important, is the tool one that supports being re-sharpened? If you are using high quality tooling to start with, chances are that the answer is yes. Second, is the tooling being sharpened on the correct sharpening equipment and to the appropriate standards as specified by the manufacturer of said tooling?
Third, are you running the tooling at the correct feed and speed? In the majority of cases, the feed and speed will not be the same as it is for the same tool as it was new. Because of the geometry change that the tool experiences after sharpening, the feed rate is generally reduced.
When purchasing CNC tooling, the old motto holds true - you get what you pay for. If you are spending the bucks to buy high quality tooling, such as Onsrud tools, you will get more than a good tool. I have nothing to gain by expressing my opinion, but I have found that the Onsrud staff and the support that is offered by them is second to none. I feel that the price I pay for these tools does not stop at the delivery of the package of tooling to my shop, but rather I have a vast network of resources to turn to when I need help, advice, and guidance. Yes, I have had problems with Onsrud tools. Some were my fault, and some were the fault of Onsrud, but in every case the customer support available from Onsrud has always been top shelf, a fact that justifies why I pay for quality tooling. I am not saying that Onsrud is the only game in town. Find a tooling manufacturer that can provide the support that is needed to accompany their product. Poor quality tooling will cost you more in the end, when things like pre-mature spindle wear are calculated into the cost of your tooling. Poor quality tooling will also cost you more in trashed parts, as you refer to in your original post. In the end, the cost per part is what you should be basing your tool purchases on and I hope that I have shown that this cost goes beyond the cost of a new tool purchase price.
We have never tried them reshapened, though. I guess that is still to be tried one day. We nest everything in the kitchen cabinets, cutting mortise and tenons for joints and the toe spacers as well. Often our sheets (8' x 4') will have between 8 and 15, counting the drawer backs, rails and other small items. Feed speed is set at 37m per min.
When we service the tools (1/2" OD), they will come back to you smaller. They will perform as new, until they get to a .465 OD. At that point, you will notice a decrease in tool life, but not before.
Don't throw out the old tool - save them and Courmatt will provide you with our recycle credit program. Any piece of solid carbide, whether it's an end mill style or an insert, we will purchase from you. The cost of carbide has risen 300% in 2 years, so anything we save (which we sell to recyclers or we service and give to woodworking schools) will save mother earth from additional mining.
I do believe you can get the same performance from a service tool. If you don't believe me, send some of your tools to us and we will service them. The only thing you are going to lose is your tooling cost per part.
When a tool heats up during the cutting operation, it does not change the structure of the tool and/or its performance once it has been serviced. The tool and chips will heat up to 130-160F during its cutting cycle. If your tool and/or chips are hotter than that, reduce your RPMs. I know you are not going to have a device to measure the temperature, but you should be able to handle the tool right after the cut cycle. If it's too hot to handle again, reduce RPMs. Remember, make chips, not dust.