Tooling Life: Assessing Cutterheads for Replacement

Straight-bore cutterheads can last a long time, under ideal service conditions. But here's what to look for if you're wondering whether it's time to replace one. April 21, 2011

Question
I have a question regarding effective life of straight bore cutter heads. We have some tooling that is still in use as of 20 years. I can't help but think I should be looking at replacing a few of these with new items. I am thinking about all the constant stresses involved. I know it can't hurt to change them Im just interested to hear what you other guys do and if you have a max service life or when you do say enough is enough.

Forum Responses
(Solid Wood Machining Forum)
From contributor J:
I would replace any head that has been in an impact. This should be fairly easy to tell, damaged gibs, head body, or big dents are most common signs of damage due to impacts. Once damaged, who knows the extent of the damage, there could be hairline cracks which might not cause a problem for a long time, then boom! I would also replace heads that have oversized bores, if the bore gets to sloppy over time you could end up with one getting seized on the shaft. I have seen many people use cylinder hones to
clean up the bore of a head.



From Dave Rankin, forum technical advisor:
There are a few factors that I consider about replacing cutter head bodies.

1. For heads with four or more pockets; have all of the pockets had knives or gibs in them at all times they were being used. If not, then you could have some potential damage of the body.

2. Size of the head. Most profiles use 4" heads and under, so these are the heads that should be looked at first (unless you have damaged heads).

3. Manufacturer of the body. There are many brands of head bodies that have to be considered. I think Mike, that most of your heads are Weinig. If so, this is one of the top brands. They use top quality metals and hardware. Some of the other brands including some imports and domestic use top quality materials while others do not.

4. Screws. If you have used a process where the gib screws were tensioned properly (correct torque and wrench size, etc.) then you most likely have not damaged the threads.

5. Bore of the tool. As already stated, the bore is critical. I use a bore test gauge to assure that the bore is correct.

6. On corrugated heads check the condition of the corrugations.



From contributor J:
When measuring the bore what tolerance do you look for? How do you determine the fit between the spindle and the bore of the cutter? Do different manufacturers of machines and cutters use different tolerances? Is this something one should measure when new then do periodic measurements to see how things are wearing?


From Dave Rankin, forum technical advisor:
Different types of heads have different tolerances in the bore. Hydrolocking tools generally range from .00025" to .001". I have seen others that are not this tight. Straight bore heads usually between .0005" and .002".

I measure the spindle with a micrometer and the spindle with an inside caliper or gauge block set. The set includes as exact size, and 1 each of .001" over and under. Tolerances vary between machine brands and cutterhead brands. If you stay within the tolerances above on new tools you should be good to go. I have had 1 manufacturer that made the cutter head bore so tight that the tool had to be returned to be opened up a little.

In general, the spindle is to be the exact size and the cutter head slightly under. If you use a good manufacturer of heads you should be fine to run from the box, I do check the gibs for balance. I check my tools for wear when I change the tools and do a complete examine including bead blasting about one per year.



From contributor S:
I have also recently bought a five head Weinig moulder and you have answered some of my thoughts. I have bead blasted some of my heads and wander what if anything you put on them to keep them from rusting? I have not had any rust yet but I do not want them to in the future. I am doing a lot of reading and have been self teaching myself about running this moulder. About 50,000 ft through so far and no major mishaps and the costumer is extremely happy with the product.


From Dave Rankin, forum technical advisor:
If you use a good grinding coolant you should be able to leave this on the head as a residue. I use Thrust for keeping my heads from rusting. I very light coat and you are good. Before using of the moulder wipe out the bore to make sure this is clean and dry.


From contributor H:
ISO has tolerances for fit of cutter head and shaft. I think H7 is a common one used by European manufactures including Weinig. This allows for tight fits that can be assembled or disassembled by hand. ISO gives a range that is acceptable. I agree with Dave that it can vary from different manufactures. We had some reduction bushings made that were so tight they had to be tapped on and off with a rubber mallet. I have noticed my US made 1 bore tools have a tighter fit than a 1 bore from a Euro mfg. Maybe the US works to a different standard of fit.