shaft body rubbing against wood?

[prettygoodnotbad]

when machining wood, with lets say a 1/2" spiral that has also a 1/2" shank, there is no shoulder, it goes from the flute directly to the shaft.  Is it bad news if the shaft/body of the tool above the cutters to make contact with the stock?  

I'm assuming this is a sure fire way of over heating the tool. Is it a never ever do this type scenario or if theres a few instances throughout the machining where this happens it can be acceptable?

[seth.madore]

It really depends on the toolpath and rigidity of the machine/spindle/tool. I try to avoid it at all costs in metal, but you MAY be able to get away with it on occasion in wood. However, I don't think the issue will be in the tool overheating, but rather, burning of the wood. 

So, my opinion? Stay away if at all possible.

[DarthBane55]

I think you'll be fine, try and and you'll see (requires 2 axial passes of course).

Also, if you use 2d contour, you can make the lower pass a little bit outside of the top pass using the wall taper option.  Put a small angle there, and when you simulate check the coordinates, and make the lower pass end up just 0.001" or so away from the wall, something small enough that you wouldn't see on the part and that would just make the shank rub less (or no rub).

[prettygoodnotbad]

@seth.madore thanks, I actually do this pretty frequently on my little carbide3d shapeoko machine without any problems, now we've got a much more powerful machine in the shop I don't want to carry over bad habits. Anyway seems like sound advice!

[prettygoodnotbad]

@DarthBane55 the wall taper is a great tip, never really clued in to what that could be for, thanks!

[daniel_lyall · Accepted solution]

@DarthBane55 NO it is not a good idea at all the cutters spin at 5000 to 26000 rpm, rubbing two sticks together will start a fire if it gets hot enough, a bit of metal and wood (burn m f burn) it is how I almost set a machine on fire from a bit of wood flicking up and rubbing on the cutter it took seconds to start burning.

Doing the cut in 2 tool paths would be way better, cut down to the full depth of the flutes and on the second toolpath have a radial stock to leave big enough so the shank of the cutter does not touch the bit of wood at all, then you can come back and do a clean up with a long cutter.

[DarthBane55]

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@daniel_lyall wrote:

@DarthBane55 NO it is not a good idea at all the cutters spin at 5000 to 26000 rpm, rubbing two sticks together will start a fire if it gets hot enough, a bit of metal and wood (burn m f burn) it is how I almost set a machine on fire from a bit of wood flicking up and rubbing on the cutter it took seconds to start burning.

 I would imagine that in wood you feed quite fast, if you were to dwell in place i guess it can burn, but if you go 300 ipm i doubt it has time to catch fire due to shank rubbing slightly.  That being said, I am not a wood worker, so I retract everything I said, don't want to be responsible for a fire...  I did mention to use the wall taper angle tho...

[daniel_lyall]

I was under the same impression once that a slight rub would be fine it burns the wood if it rubs it may not catch on fire but it leaves burn marks that will make the cut look burnt the OP is going to be doing production with long cutters in walnut. 

[DarthBane55]

Ya, well for sure i agree that a cutter with a long enough flute to cover the wall is much better, no doubt about that!  But I thought that OP wanted to do this because he did not have such a cutter.  Maybe I assume too much, you know, like he was in a bind, no time to buy a cutter, "what can i do to get it going" kinda thing.  Leaving 0.001 on lower cut might have worked without apparent line on wood (wall taper angle), it was just a little trick to try.  But, if a tool with long flute is available, that is for sure best.  Or undercut the shank on the tool if a tool grinder is available too.