Troubleshooting Chatter And Snipe

      Is it a knife grinding issue or a moulder set-up problem? April 10, 2005

Question
I'm a tool grinder for one of the top cabinet companies in North America, and have been grinding tools for them for 6 years. I have three types of grinders.
1. Deihl - Used for rough grinding profiles only
2. Rondamat 960 - Used for straight knife sharpening
3. Rondamat 970 - Used for profile sharpening.

Then we have 6 Weinig molders. We are starting to have some problems with a few things.
1. fuzzy parts
2. chatter and or snipe
3. tear out

I've been grinding the same way for the last 6 years, using the same style of moulder heads. We use North American hydro lock molder heads with a 10 degree hook, and we use optic steel (WKW) for our HSS and some piggy back cutters. I was told it might be a balance problem, and I don't know how it could be, when I balance the gib screws, gibs, and knives to within .1 of a gram of each other. I was also told it's the way I grind the tooling, which is the same as when I started 6 years ago. If anyone has any info that can solve this problem, that would be great.

Forum Responses
(Solid Wood Machining Forum)
From contributor A:
You said you are the tool grinder. Do you set the moulder up as well? It might not be your fault. The snipe is the moulder opís error. The fuzz and tear out might be too but if nothing has changed then your lumber might be improperly dried. Your 10 degree hook might not work the same for you if you started working with a different type of wood recently. My experience with chatter is, when it starts, everything else comes as well - chip out, etc. Itís easy to blame the grinder guy but when you are the grinder guy and moulder guy, you kind of know something isn't quite set right. I think after six years, you know what youíre doing.



From the original questioner:
They did give us one new species of wood which is Alder, but this occurs on all species. I'm not a moulder guy, just the tool grinder. I do try to do some set ups on the moulders but it is hard when I sharpen 30-35 moulder heads a day plus fix others that have been crashed or damaged during off shifts. So to you it sounds like moulder problems? Whatís your opinion on this? On profiles, Weinig techs say when grinding them at 27 - 30 degrees then finish grind then at 25- 26 degrees, even with a CBN wheel. Now I've tried both ways - grinding the way Weinig said and grinding at 27 degrees and not finish grind them at 25 degrees - and I see no difference in the finish cut off the moulders. Is there a good reason for the finish grind or is just a waste of time?


From Dave Rankin, technical advisor, Solid Wood Machining Forum:
I agree with contributor A, the lumber may be part of the problem. When it comes to chatter and tearout, this is normally caused either by the lumber conditioning or the lack of proper holddown on the moulder. Over the years, there have been many new developments.

The first that will help with the tearout is the use of shear angle cutterheads. I have used them for many years and you can do both straight and profile knives in them. Another development is the DGK tool steel. It has an advantage over other steels because it has the extremely hard surface on its face. It is ground using normal grinding wheels and jointed with normal jointing stones. Its advantage is that you can increase the angle of the back clearance and still have a knife that holds up against the cut. With other tool steels, when you increase the angle to try to reduce tearout and chipping, they have the negative side effect of less run time. The tool dulls quicker.

I think that the first place to start is with the setup of the moulder. Are the fences straight, are all of the holddowns in the proper location and parallel, and are the belts in good shape? If you are using outboard bearings, are they aligned correctly?



From contributor B:
I also work for one of the top cabinet companies and have been a tool grinder for 10 years, grinding carbide inserts as well as moulder tooling. In fact, I work for the same company. We are not doing a really bad job grinding but when you are running tooling at high RPMís, like a moulder, you have to take into account all the little things.

We are currently grinding our knives at one angle, no finish grind, with a 2mm borazon wheel and weíre not grinding axial constant because they donít think it will be beneficial.

It doesnít take much longer to grind axial constant. We have the equipment to do it and it would benefit both the moulders and the tool grinders right? The biggest finish problem is the moulders - right now some of the spindles are as rough as a corn cob and have had too many heads spun on them. I didnít bother checking the run out since the spindle felt like a corn cob. I didnít think I needed to look much further to know we have a problem.

Now all the hydro heads have been sharing the corn cob spindles so now theyíre pretty much crap too, or are at least no better than a straight bore head and probably worse when you pump them up on a crappy spindle.

I told them donít take my word for it - call the Moulder Doctor. We have 6 moulders so youíre talking a lot of money to replace all the spindles at one time so I recommended we start by replacing the top spindle doing the profiling since this is the hardest part to sand and purchasing heads that will only be used on this good spindle. Then if they do spin a head on this good spindle, replace the spindle and move the one that had the head spun on to a less critical spot. They have not noticed any difference in the past because they have not seen what a new hydro head and new spindle can do on a moulder that is in top shape

Now - grinding the cutters - cutters need to be clean, wiping the bore clean of saw dust or whatever. I prefer using ceramic or a vitrified grinding wheel. They are more cost effective and you can dress them, keeping the wheel the same shape as your pin and more accurate. However I am not opposed to using an older out a round borazon wheel to do the back clearance angle and then finish grind with a new borazon wheel so the profile is exactly like the template. Itís not as cost effective but easier for less experienced tool grinders.

Most of the species we run are fine with a 10 degree hook head except alder. This should be a 20 degree head ground with a 30 degree back clearance angle and maybe a 28 degree finish grind?

These are a few of the things I think we need to do. I donít want to make this too long a post so I will stop here and any input is welcome.



From contributor C:
Iíll cast another vote here for the chatter and snipe being a set-up related problem. I would also suspect that maybe a little bit of the tear-out problem could be a result of less-than-optimal set-up and/or machine condition. Fuzzy parts, well, I've always found alder to be a little on the stringy side anyway. Could this be what you're referring to? Moisture content is also a possibility. Has this been checked out?

Six moulders, wow! I can't imagine how many operators those machines have seen over the years, with the moulder events being some multiple of that number. Anyway, sounds like there is more involved with your problems than simply the choice if hook and grind angles, and what wheel you choose to use. Eliminate the other variables on one of your newer (least abused) machines, then you can experiment with grinding angles and such.
Maybe your production manager should schedule a big pow-wow. Your concerns regarding your product quality, as tool room guys, is commendable.



From contributor A:
I don't use a finish grind either. I used to but I went to a Wadkin seminar (I use Weinig) and they didn't use one so I tried it and it is very time saving and I really think the knife life is a lot longer.

Obviously, you wouldn't be here if you didn't care, and your co-worker too. I think you two should bring the condition of your moulders to the bossís attention. Corn cob spindles? Who trains these guys? Isn't spinning a head the one nightmare that is tough in the beginning? You guys know your stuff, and your company relies on that. Let them know whatís going on.



From the original questioner:
I would like to say thanks for all of the info you guys have been giving. You have been very helpful. So basically what everyone is saying that right at this point it's moulder problems and not the tooling. We need to do a better job training on the moulders and fix them before trying different hooks angles and wheels in the tooling room.


From contributor D:
As the others have said I too believe the problem with chatter and snipe are machine related. The fuzzy sounds like lumber or possibly knife grind to material problem. Approaching these problems and getting definable and clear results may be a greater challenge.

When planning some solutions on the moulder, clearly define the difference between set-up and maintenance. It sounds as though both are in need of help. I realize there are many people out there with experience and training available, but don't count Weinig out as a resource for extended training. They have an award winning program for moulder set-up training. These classes are going on all the time, just call Weinig to see when there is room. Of course having a Weinig tech stop in and look things over is always an option. Call the service department and try to set something up.



From contributor A:
I just read through the posts and raised an eyebrow. Ten years ago, Weinig taught me to grind a 25 rough and a 20 finish grind. I see the degrees have changed a bit. You opened me up to some new experiments.


From the original questioner:
To contributor A: Right at this point they still want to start in the tool room. We are going through all the moulder heads (150+ heads) to make sure they are balanced to .1 of a gram knife to knife and then we are stamping the pocket and gib with the same number. We are also making all new templates to get ready to grind axial. Then we are making 2 wing cutters into 4 wing cutters, but the feed rate is going to be the same as the moulders. Iíve got a feeling we will have burning problems then, but they don't want to listen to me. As for a finish grind thatís not going to happen until they get the moulders fixed first because with the run-out they have, no one will be able to tell any difference. I will keep you posted on progress.

This question is for everyone. I have a Rondamat 970 and we use a 2mm CBN wheel. Can you use the diamond wheel dresser (not while it's running) to center the wheel into the hub? And will it center it to the tracing pin? If not, why?



From Dave Rankin, technical advisor, Solid Wood Machining Forum:
I use the diamond dresser, while the grinding wheel is stopped, as a guide for centering the wheel. I use plastic shims to perfectly center the wheel. If the wheel is not centered then the side clearances will not come out correct.


From contributor E:
You mentioned the use of gibs, so I'm assuming these are not cemented or braised cutters. If you are only indicating radially, you may be out-of-parallel, axially. Also, if these cutters are counter-bored for tapered split-collets, check the heads tapers, then the collets. Check for nicks and burrs on both, and at the split in the collet.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
If you are having trouble with a top head it could be a pressure shoe or chip breaker issue. Too little pressure will allow the part to move. Also improper pressure shoe alignment to the bed plate can cause issues with top or bottom. Bottom chatter can be pressure shoe issues or the bed plates are moved too far away from the cutters. If this is a Weinig and you have a student handbook read some of the solutions to chatter problems or call Weinig they are always very knowledgeable and helpful. The fuzz with alder is a constant issue. While the 20 degree hook and 30/27 grind angle will resolve some of it, it is a constant problem because of the wood and the moisture content.



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