Cutting a half pillar

[mikejohn]

This is an Autocad drawing of half a pillar.
6138.gif
It is 50cm long 8cm wide and 4 cm thick in beech.
How easy will it be to cut this piece? (ShopBot will soon be here
)
Normally done on a lathe, but for construction purposes I would like to make it in 2 halfs.
Any hints would be appreciated.
......Mike

[paco]

I would suggest to continue doing it on the lathe and just cutting it in half on the table or band saw... to machine such a part with the PRT, you would wish to have an indexer... doing this in 3D would be a waste of time!?

[mrdovey]

Mike...

It's actually fairly easy to cut. You'll probably want to use a round nose bit and make longitudinal cuts. I've created a couple of web pages that may help somewhat. On my PRT-96 this would take between six and seven minutes using a 1" round nose and spacing the cuts at 2º.

...Morris

[paco]

Hello Morris!

...curious; which of your pages are you refering mike to?
I guess you are using an indexer right?! Or have you a lathe installed on your PRT? This late option, I wonder if it could be done and efficient...? ...once installed on the table, the lathe could be used to turn the blank and the PRT used to machine on it; doing only 2D (X&Z or X&Y) moves to follow a patern... hummm... a new project to think about...! sure this would'nt be like having an indexer; more like a standard lathe with an automatic patern "follower"...

[mrdovey]

Paco...

Nope. Imagine having a template for a lathe duplicator with a straight edge on one side and the part profile on the opposite side. If you imagine the flat side running along the bottom center of the blank, the profile describes a cutting profile. Now lift the profile edge a small angle - and you get a second cutting profile. Repeat until the template is lying flat on the other face - at which time you've cut that profile in the round. The very easiest case is a cylindrical section, which uses a straight profile edge. Here's a photo of a quarter-round blank cut into a 2"x4" piece of construction lumber:

6140.jpg
The web pages are those that deal with cove geometry; but a round is actually the same problem (with the curve inverted).

This is one of those things that's a lot easier to describe with pictures than words; but I hope I've helped some.

...Morris

[paco]

Okayyy...
Interesting! Well, I'll have to study your pages some more; math is as far as school is!! Seriously, this inspire me for some new projects... again! I'm now thinking about "special" mouldings; like the one you got just above... I'll be back if I find something good to use with a 2D design from a CAD...

[mrdovey]

Paco...

It's not as difficult as it would seem at first glance. It's been 45 years since I studied geometry, trig, and algebra in high school - but it's a bit like riding a bicycle - it comes back quickly.

CAD is a tool - something make work easier. It's even a /good/ tool (I used my CAD package to make the drawings on the web pages) - but CAD isn't the whole toolkit. The most powerful tool we have is the one that sits on our shoulders. (-8

I've been working on another web page showing how to make the calculations for cutting rounds (actually, it's done except for the drawings) and I'll add that to the CNC menu page when they're done. It takes me a day to put a set of drawings together and I just haven't been able to take the time.

...Morris

[beacon14]

If you are fluent on the lathe the technique for getting half-columns is to glue the blank up out of two halves, with a piece of paper glued between the halves. After turning, you can split the blank apart at the paper using a wide chisel and mallet.
A light pass over the jointer cleans up the paper residue.

[garyb]

As with Morris this is an easy cut.
We cut similar profiles all the time but on a larger scale from cedar beams, usually 8x4 x 48" and 96" in length. Depending on the amount of detail will take under an hour with 1/2" ball end.
Photos must be on the other computer but here is one of a rope pattern which is similar in cutting etc. Size is 6.25 x 48" cut with .25 ball end in about 35 mins or there abouts.


6145.jpg

[mrdovey]

Gary...

Oooo! Nice! (I like it.)

...Morris