Need desperate help....Ragedy Edges

[rossi07@mindspring.com]

All of a sudden my shopbot is routing really rough and radegy edges...Routed in letters unsmooth..and borders edges real rough..Any one experience this...or know how i can fix it..

[mb.finearts@virgin.net]

Sounds like it could be blunt tool, shot bearings in the spindle head or loose parts on the rest of the machine. Simple to rectify, tighten or replace the ofending item. Or have you changed either the spindle speed, or the travel speed....
Martin

[studebaker]

I had this problem once.... it was a loose allen setscrew on the pinion drive gear of one of the stepper motors!

[Dick McGuire]

Had the same problem and it came out to be bad bearings in the router.

[jkforney]

Rossi

I think you may find the problem to be one of the above. Very rarely does something suddenly happen that affects the cut quality as drastically as yours that isn't mechanical. My bet would be the set screw on the pinion. Even if that isn't the problem putting some blue (not red) locktite on the screws is not a bad idea (yes I know shopbot sends them with some on the screws). Let us know how it is coming.

John Forney

[gerald_d]

If the set screws are not tightened square on to the pinion flats, they come loose very easily. The trick is to "nip" the screw slightly against the pinion and then "wiggle" the gear to see if you can find a looser position. Continue the nipping and wiggling until you have found the flattest (lowest) point - then TIGHTEN.


8467

Loctite? Sorry, don't believe in it for this application. IMHO, Loctite only slows down the rate at which a joint comes loose - it does not prevent loosening. In safety critical applications it is good because you should detect some freeplay before the whole joint falls apart.

If one of Rossi's pinion gears have come loose, then he won't see raggedness in all directions of movement. . . . (unlikely that both x and y have gone simultaneously)

[frank]

Rossi,

There are number of things that may be causing your problem and all of the above suggestions are good places to investigate. It is most likely mechanical. Pull on your router bit to check for any looseness there. If you feel any movement, then it is a matter of tracking it down to a loose bit, set screw, etc. If none of these suggestions leads to a solution, give us a call and we'll see if we can find the cause.

[flyboy]

I'm having the same problem but I think it's my cutting bit. After a very short run of parts it's tearing up the last layer of plywood. I think I need a down-spiral. Any ideas or sugesstions. I'm running .4 ips 1/4 birch plywood with a 1 1/2 porter cable at highest speed. (adjustable by harbor frieght speed control very nice and smooth - $10

[gerald_d]

Tom, our experience is only with 1/4" bits running around 25 000 RPM. And we always get great cuts with the Belin spiral bits.

The life from these solid carbide bits is at least 10 times greater than straight carbide tips or spiral high speed steel bits. There is simply no comparison. (We probably get 30 hours cutting time per bit in 3/8" marine ply) The downside of Belin is the price of $16 for a 6mm bit at the factory in France, and nobody has yet been able to resharpen one like new. Belin will resharpen at $13 per bit in France. Because Belin is a metric company, their metric sizes are cheaper than inch sizes.

The Onsrud bits would appear to be the American equivalent of the French Belin, but I have zero experience of them.

Back to the ragged edges; A cheap bit can go blunt within 20 minutes. The bigger bits may be going too fast at the tip speed - especially if the bit was meant for metal-cutting (hardly any rake angle). Tom, you did say that your problem starts after a short run, and this sounds like a bit going blunt. Have you ever tried a Belin?

[tlempicke]

Your problem also may be related to heat. If you are cutting at .4 inch you may be generating a lot of heat at the bit. Look at the chips the bit is producing. They should not be fine sawdust but actual chips that the bit has cut.

[gerald_d]

PS. The 0.4 ips sounds very slow - we generally go about 1.5 ips with the bit I mentioned above.

[jkforney]

Gerald

Re your message "Loctite? Sorry, don't believe in it for this application. IMHO, Loctite only slows down the rate at which a joint comes loose - it does not prevent loosening. In safety critical applications it is good because you should detect some freeplay before the whole joint falls apart. "

Shopbot ships the tool with a form of locktite on the set screws (micro encapsulated I think). I put additional red locktite on my machine and those that I have assembled for others. As far as a joint coming loose with locktite, you seem to imply that with locktite a joint goes from tight to total failure. This simply does not happen. I think locktite is a solution to the problem of loose set screws. I haven't had my set screws loosen for the three years on this machine. I guess we will have to agree to disagree on this matter.

However, you are certainly correct that the screws need to be flat and tight against the flats and your example should be incorporated in the shopbot manual.


John Forney

[gerald_d]

John, my experience with Loctite is that it more often than not gives a false sense of security. We can use my sketches above to illustrate this - if the screws had been loctited while sitting in the "bad" position, they would still feel tight after the gear has moved to a loose position.

"you seem to imply that with locktite a joint goes from tight to total failure" Oops, I didn't say that, did I? For a screwed joint to come loose we first need some slight movement between the parts being held together - this tiny motion then gets the nuts/screws to start turning. Loctite will stop the nuts/screws from turning, but it does not stop the slight movement that is already in the joint. If the screws were big and tight enough to start with, there would be no movement in the joint and the fasteners would not come loose.

In different words, looseness develops in a joint before the screw threads want to start moving (tip of set screw against the shaft in our case). Loctite will prevent the threads from loosening, but it does zero for the initial problem.

Without loctite, the screw would start turning loose and this gives a rapid deterioration of the joint. With loctite, it may take days before you notice that there is looseness in the joint.

When we test new products in our automotive industry (my real paying job!) we do the fatigue and endurance tests without loctite. Then we really know if the design is good. However, then we specify loctite or nylock nuts in places where we want bolts never to fall out, even if they did come a little loose - like steering linkages and suspension. Loctite is also specified where we want to keep water and corrosion out of a threaded joint - i.e. so that it can be loosened easily. How's that for a contradiction?


Back to Raggedy Edges now?

[donchapman]

Double check that both of your x-axis stepper motors are working. One of mine became disconnected at the wiring coupling nearest the motor and wreaked havoc before I realized what had happened. The machine keeps routing but with distorted and uneven cuts.