Reverse V carve brain teaser

[Mark Bolton]

I have a production job coming up that will require a shape to be cut out of a part 7-8 inches wide x 16-18 inches long that needs to have fairly sharp points on the exposed face. So imagine a board with an internal shape cut out that has many sharp points. This wont be possible from the front side face with a spindle and would have to be machined from the back side. The customer asked for 3/4" thick material but is willing to go thinner. Our thought was to V Carve these but from the back side. Where the V bit would carve down and pierce barely through the bottom face leaving a relatively sharp point. Those points would be pretty thin and fragile.

There is no entry point for a band blade. Or to have the customer go even thinner (which they dont want to) and have them burned out on a laser capable of the thickest material we can.

I have tossed around hogging out the bulk with a clearance toolpath and doing a finish profile with a tiny endmill but even with a 1/16" (1/32" rad) tapered ball nose you lose any sharp points.


Im overthinking at this point..

[David Falkner]

Is it possible to do the hogging on the CNC and use a laser to cut the very fine point they want? Obviously better if the CNC also has the laser mounted because the difficulty would be in getting registration perfect with the laser coming after the CNC cut if it is two different machines.

David

[bobby milam]

Not picturing exactly what you are trying to accomplished but is it something that you could accomplish like in a vcarve inlay? One side is carved in and the other out? That's what popped in my head when I read your post.

[Gary Campbell]

Mark..
I assume there is some IP attached to your job, so I wont ask you to post it, but, can you post a pic of something similar?

[Peter Froh]

Maybe just the illusion of sharp points. Cut out the shape then do a final pass with a vbit cutting the outline of the shape to make the surface look sharp.

[Mark Bolton]

The illusion of the points was the only real solution I could come up with and wasnt quite accurate when I said V carve toolpath but meant as Peter stated, clear the bulk of the material and then just do a profile-on with a v-bit. This isnt the actual file but the shapes are simply random curved points but trying to get them fairly sharp on the front face of the part. smcpoints2.jpg

Using a 60 degree V bit from the back you get something like this smcpoints3.jpg

From what would become the front smcpoints4.jpg

[Mark Bolton]

As an addition, we tried the profiling with an insert V bit, no go. This is in solid wood and with the angle of a V bit (60 degree) the positive points (I didnt draw any in my example images) just get too fragile and snap off. We did have some success with a 1/16" tapered ball nose.

[Rich Lester]

Assuming that the profile has to be a through profile, could you create what you have shown on two 3/8" thick pieces and add some corresponding shallow dowel holes for location apply glue and flip them onto each other to provide a 3/4" thick part. Not sure if this would get you what you need but it was a thought.

[Mark Bolton]

That would surely work Rich but this is one of those typical bean counter jobs that needs minimal ops (i.e. keep the cost as low as possible). I think we have something workable with the 1/16" tapered ball nose and a back relief that may work. Couple samples went out next day air this afternoon so we will see.

[Ian Stewart-Koster]

Why can't you laser it?

We've recently finished a job that ran for 23 hours, lasering fine letters out of 20mm MDF.
It was yucky stuff, but it worked well.

The coarser stuff where radiused inside corners were not objectionable, we routed, but the finer stuff went well on the laser.

[Mark Bolton]

Why can't you laser it?

We've recently finished a job that ran for 23 hours, lasering fine letters out of 20mm MDF.
It was yucky stuff, but it worked well.

The coarser stuff where radiused inside corners were not objectionable, we routed, but the finer stuff went well on the laser.

That would work other than not having access to, or anyone locally, with a laser capable of cutting 3/4" material.

We have a solution that will likely work using a 1/16 tapered ball nose and have the toolpaths down pretty short and getting shorter.

Still looking for options for the inside points but we may get by.

[Brian Lamb]

Without knowing the exact shapes, it's hard to say, but I would route from the back down until the thickness to the bottom was say .100" then go to the laser and finish the profile. Or another thought, using your angled cutter approach, just run it 1/16" undersize and then use the laser to straighten up the edge and make it stronger so it's not a fragile knife edge surface. Laser will do down to about a .004" -.006" kerf, so your corners would be as sharp as they will ever get.

[Mark Bolton]

Without knowing the exact shapes, it's hard to say, but I would route from the back down until the thickness to the bottom was say .100" then go to the laser and finish the profile. Or another thought, using your angled cutter approach, just run it 1/16" undersize and then use the laser to straighten up the edge and make it stronger so it's not a fragile knife edge surface. Laser will do down to about a .004" -.006" kerf, so your corners would be as sharp as they will ever get.

If I had that option I would but we have no laser in-house, and we have no access to any laser with the capacity to sub the job out within 100 miles. Hence trying to make due. I think we will be ok with the small(ish) rad left with the tapered ball nose cut from the back side. Any V bit from the back leaves too fragile an edge and seem to split off the male projections in the profile (my sample images really only represented female cuts). If you imagine a long slender male projection out into the pocket (a long slender point). Nearly any amount of tool pressure will snap off the point on the long grain running perpendicular to the cut.

We have changed the cut profile substantially and its looking now like the tapered BN is the answer as its only making a super slight cleanup pass beyond a straight clearing tool.