lost the blade

[jacquesm]

Not a very good day...

It started off well enough the first 5 passes were done pretty quickly, we're getting the routine down pat, just up & down the stairs every half hour to load the next pass toolpath and check the machine.

Then, on the very last pass it got scary. The last pass is run with a ball bit, the other passes with a square carbide bit. The ball bit is a bit like a drill with a half globe for a point, it has all the characteristics of a drill, including 'pulling down' into the material. It also vibrates like hell. So, the router was slowly but surely pulled down until the ring of the router housing touched the ring of the mount. Just before I stopped it the router was doing 1" cuts...

Total drop was 17 mm. I realised something was not quite allright when a hole

started to appear in the blade, by then it was too late so I let it run for a bit longer to figure out what the hell was going on.

After that happened I spent the rest of the day reworking the toolpath so that

we can use the square bit for the whole blade. Ron spent the rest of the day working out a better blank that uses much less wood, we'll try to do a short version of blank and new blade routine tomorrow to see if we got it all right.

I also noticed a really nasty bug in the equidistant routine (toolpath correction) that  I originally used for the ballbit.

Oh well, we'll try again tomorrow. But it is depressing to be this close, almost have a working blade only to lose it all.

Pictures follow:

Hole in the blade:

Crosssection, front of the blade:

Crosssection two, better view of the profile:

[BT Humble]

It looks like a high-quality product (well, once you make one without the hole!) but isn't that a seriously steep angle on the tip?  I mean, I would have expected to see a couple of degrees at most, but you look to have nearer to 20 there.  

Or is it a low-speed-high-torque design?

BTH

[nack]

Jacques,

I think you might want to consider swapping your router holder for one made from the porter-cable fixed base with a rt angle adapter screwed on where the plastic bottom plate belongs.  The P-C base gets a lot of grip when you tighten the clamping screw down on it.  I almost posted this when you got the new router and put up the article about modifying your tool holder, but I didn't want to come across as one of those "I can do that better" types.  I have never built an overhead router-bot, but I have made a few router tables by just screwing the P-C fixed base to the bottom of a table, and I can say I've never had any slipping from the base - even when cutting extemely tough woods.  Not telling you how to run your show, but please consider that with that whole sleeve tightened around the motor housing there is a lot more friction than you have with just a couple grub screws holding it, and as an added bonus you can use the depth scale on the base, as the spiral groove for the guide-pin is calibrated to the scale on the fixed base.

It really is a beautiful thing you've got going there, and I am sure that this little glitch won't slow you down for long.

[jimovonz]

I believe that he has rotated the entire blade to make better use of the material.

[BT Humble]

Ah!  That makes a lot more sense.

BTH

[jacquesm]

Thank you Nack, that's a pretty good plan and I'll look in to how I could do that using the original base, you make a lot of sense ! One problem is limited space and very limited carrying capacity, the motor that 'lifts' the whole rig is at the edge of what it can do, so any mount would have to be fairly light.

We did change the mount a bit, now we're resting on the 'top' part of the router housing so it can not drop any lower, and we've added some rubber to the mount to catch the vibration.

Another possible problem is that it might position the router further out and interfere with the blank / posts on the table.

Even so, I think that's worth investigating, it might not work for me but it sure beats my homemade clamp by a mile or so