Interesting day

So we invested in the CNC last year and have been making good use of it but I guess old habits die hard. We have a job making a bunch of mobile/desks/tables for a school, 42" square, Hard Maple (the devils wood), dual locking casters, arched aprons. I have always made arched aprons, cathedral and roman arched doors, etc., on the shaper. Cutter block, rub collar/bearing, sled, template, destaco clamps, sacrificial backer to reduce blowout on the outfeed side.

Set the whole thing up today and roasted 4 aprons to either gnarly grain, catches, or blowout. All hand feeding a sled through the shaper. Steep exit angle. I hate hard maple.

4 aprons in I glance over at the CNC running other parts and Im like... what the heck were you thinking idiot?

Walk in the office, draw up a dog boned pocket fixture in a 1 1/8 MDF scrap, and the profile tool path for the arch with a 3 pass raster using a 1/2" down spiral, profile last, and proceeded to stand there in complete comfort, loading aprons into the fixture with no clamping (due to the down spiral and a press/mallet fit in the MDF jig) and run all the aprons for 12 tables while Im machining other parts, doweling, and so on.

Old habits can be hard to break.

It was so easy it was shameful.

It sounds like you had a good day!

Yep, there are so many days when I say to my wife "I love having a CNC router". Things which would have taken me hours by hand taking just minutes or seconds by CNC and more perfect than I could ever get.

Great work on CNCing a step in your production!

They are certainly amazing machines that work hard and can make your days work more enjoyable.
CNC Routers are fun to run :)

Guys, I don't know much about cnc. Could someone please explain why the same cut was easier and cleaner on the cnc than the shaper? I keep thinking that the cnc's I've seen are routers (often similar to a regular woodworking router) and it's the very same knarly grained wood. Why did it work better on the cnc? Does the computer take much lighter cuts, are the bits different, or what?

Thanks for teaching me.
Fred

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Originally Posted by Frederick Skelly

Guys, I don't know much about cnc. Could someone please explain why the same cut was easier and cleaner on the cnc than the shaper? I keep thinking that the cnc's I've seen are routers (often similar to a regular woodworking router) and it's the very same knarly grained wood. Why did it work better on the cnc? Does the computer take much lighter cuts, are the bits different, or what?

Thanks for teaching me.
Fred

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Fred,
To me, its in part because of the rigidity of the machine itself as well as the fixturing. If you imagine hand feeding a part across a router bit or shaper cutter with a bearing and a template for instance, you hit spots where from all the standard grain issues, the part wants to catch or blow out. The cutter may try to split off shards of material along the grain where you simply couldnt by hand use mabye climb cutting to minimize the problem.

With the CNC the part, and the tool, are rigidly fixed which effects cut quality tremendously. Additionally, in this case, you are able to use a spiral bit with multiple passes which is also cutting in a shearing action forcing the piece down into the fixture. So in the case of these arched aprons, we made the fixture the exact shape of the blank. On the first cut the CNC cut out the arched profile on the blank as well as the lead-in and lead-out on the fixture. So fragile end grain cut right at the edge of the steep exit angle is completely supported and therefore cant blowout. Even with making a really good fixturing sled for the shaper, and relieving all but 1/32" or so of material with the band saw, that last few inches of end grain cutting with a shaper and sled can be a bear. With the CNC, it was a joke. You can also implement little tricks like where the profile cut begins. This is handly because you can plunge in a sixteenth or two in-front of the fragile area so that when the router comes around to finish the cut its only milling a very small amount of material from that most fragile spot.

And as stated above, every single part, comes off identical.

Funny while running these. One of my guys watching the cnc waste away all the material in the arch said "wouldnt it be faster to just trace the arch on the piece, cut it on the bandsaw, and then go to the oscillating sander and sand the arch smooth. This would include the radius ends and about 36" of flat bandsawn area (its a racetrack arch not an ellipse). I said "wanna race"? It took about 15 seconds for him to realize the work involved and that every part would be inconsistent to say "I get it now".

I get it now Mark! Thanks for taking a minute to explain it! :)
Frex

Mark, you are so right about changing the mindset to use the cnc where appropriate. It's not always the right tool but when it is it is a game changer.

I like the concept of the press-fit jig. How do you hold the jig to the table?

Frederick, another advantage of the cnc is that you can climb cut in situations that would be tricky or unsafe with a shaper. I often climb cut for hogging and clean up .010" with a full depth conventional feed.

Kevin, the mdf scrap we made the fixture out of was like 22" x 60" so we just sent all the vacuum to the front two zones and it held fine. I had skinned the spoil board that morning so that was a plus too.

We are usuallu able to hold down to about 12" x 12" with the vac for anything other than the most aggressive cuts.