Thread: Repetitive cutting in a ski base

what you are attempting is much more complex than it looks.

for starters, those crescents are deep at the front and zero depth at the rear -- if you don't have a CNC this requires that the router be mounted at a shallow angle to the work piece. It's probably best to use a cutter sized so that each crescent can be cut by plunging rather than moving the router.

ski edges are steel -- it's best to avoid cutting into them.

a ski base is a type of plastic. You may need to experiment to find the best rotational speed for the material.

I'm thinking some sort of indexing jig.

Forstner bit in a drill press with a tilting table. Make an indexing stop to index against a previous hole and an extended support for the length.

Thanks.
I've got the bit and router angle sorted. Practiced on an old clunker.

if the shape needs to be a crescent, and not a simple segment, then perhaps the inclined jig will need to allow for the router to be rotated about a point on the jig.
But I'd still use an indexing table (or similar) to maintain consistent spacing.

Originally Posted by Bohdan

Forstner bit in a drill press with a tilting table. Make an indexing stop to index against a previous hole and an extended support for the length.

I didn't give all the details of the work piece Bohdan, and they have an effect on mounting. The ski is bowed, waisted and also thicker in the middle than the tips. It's possible to mount it on the work bench producing a pretty much flat base.
The centre point of the bit may also foul the ski base but I like the idea of the long cutting edge of the Forstner bit.

Originally Posted by ian

if the shape needs to be a crescent, and not a simple segment, then perhaps the inclined jig will need to allow for the router to be rotated about a point on the jig.
But I'd still use an indexing table (or similar) to maintain consistent spacing.

A segment would be fine and is in fact what the model displays. I'm getting crescents by using a straight router bit the bottom cutting edges of which are slightly dovetailed and not full radius (but for the application crescents might in fact be better). A trip down to Timbecon threw up nothing different by way of bits.

Just a bit of packing under one side of the router base is what's producing the tilt.

Sooo, not sure what you mean by an indexing table here Ian. A Google Image search throws up rotary jobs.

If you are going to use a router then I would suggest using one of the Euro hinge hole drilling bits. They give a flat bottom and a clean edge.

Thanks for that tip.
Damn, I asked at Timbecon if they had a flat-bottomed bit. Nah. Though it might be a size issue. I'm trialling 3/4" and 1".

Originally Posted by rsser

A segment would be fine and is in fact what the model displays. I'm getting crescents by using a straight router bit the bottom cutting edges of which are slightly dovetailed and not full radius (but for the application crescents might in fact be better). A trip down to Timbecon threw up nothing different by way of bits.

Just a bit of packing under one side of the router base is what's producing the tilt.

Sooo, not sure what you mean by an indexing table here Ian. A Google Image search throws up rotary jobs.

not sure what type of ski you have there -- the skis I'm familiar with are wider at the tip and tail than the waist.

I'm assuming that the ski will be supported on some sort of stand that will hold the surface to be milled flat and level.
The indexing jig / table might be as simple as a row of screws or nails that locate the router carriage as you move it along the ski.

I have both 20mm and 35mm Festool router drilling bits.

Thanks.
Apart from the centre point do they leave a flat hole?

Originally Posted by ian

not sure what type of ski you have there -- the skis I'm familiar with are wider at the tip and tail than the waist.

I'm assuming that the ski will be supported on some sort of stand that will hold the surface to be milled flat and level.
The indexing jig / table might be as simple as a row of screws or nails that locate the router carriage as you move it along the ski.

Ok. Thanks.
Yep. See my post of 5.03pm.

Speed runs, Ern? I gather the bike has retired?

Nooo Andy!

Gone backwards though. For the first time the new bike's cc's were way fewer than the old. Riding a Husky Terra 650 now and really enjoying getting out into the mountains.

So anyway, to this point I've been working on the cut geometry and got pretty close. Desired depth at the front is 0.5-0.75 mm. New 3/4" and 1" straight bits at a tilt (using the highly sophisticated proof of concept pictured below!). The 3/4" is cutting some nice clean crescents. The 1" is cutting some rough C's and wandering while it does - it's a Torquata. Cheep cheep. The wax coating came off as I was pulling it out of the box with messy results.

Following bohdan's suggestion a trip to the local ind'l supplies place was intended to show what a hinge boring bit looked like in the flesh. However it revealed a Carbitool bottom cutting bit - as per a straight bit but also with a cutting edge running the diameter of the bottom. That will produce segments which are going to be very close to the model and a centre point won't need grinding off.

So anyway, something like a cribbage board is how I imagine Ian's indexing table, controlling spacing from the ski tip. Going for a 3/4 bit I'm thinking 3 or 4 columns and not fussed about them following the sides and curving.

There remains a decision about the extent of the pattern (density, length, placement in relation to the centre line) and there's 3 factory-made pattern-base skis in the kit to learn from.

The whole point of this exercise is that factories put too long a pattern on for these skis' application and I can roll my own.

P1010465.jpgP1010466.jpg