View Full Version : A challenging part

11-11-2008, 10:44 AM

This is a handrail with an integral cap for the newel post. It's about 4 feet long and 4 inches tall. It looks simple at first, but I keep hitting challenges.

If I do it two sided, then it will have to be oriented on its side, which is fine. Except that then there's no way to do the hole. The hole mates with a dowel turned on the end of the newel post itself. Someone else is doing the post. Also, the bottom surface needs to be flat, so I'll have to find a straight ball nose with a CEL of at least 2 inches.

I could use the indexer, but I still don't know about doing the hole, or getting the bottom flat. It seems like I might need a separate 2D drawing of the outline and hole. Then I could do the bottom and hole as a separate 2D operation. I would have to modify the 3D model to include a little extra material on the bottom. Does that make sense? Is there anything I've overlooked, or any alternate approaches?



11-11-2008, 11:31 AM
There is no way for me not to sound like a smart a@@ so I apologize in advance...

Have you thought about using a drill with a spade bit for the hole? I'm told this method works well.

PLEASE excuse me...I'm a stairbuilder and make parts like this all the time so I'll just ask these questions and make my point.

Is the CNC the only tool you own? If you are asking about getting the bottom flat I'm assuming you do not have a jointer. The basics (i.e. table saw, jointer and planer) takes care of the finished blank.

The opening cap is usually a separate piece that you attach the rail to...although your connection between the rail and cap is so tight you could just turn the cap as a separate piece and cope the straight rail to die into it using a hanger bolt to get it nice and tight.

MAKING the straight rail with the bot...personally I would make a 5' blank. Then I would take a scrap piece of OSB or MDF and make a groove to fit the blank into. Make 4' of the profile on the first side. Flip the blank over (you have a good 6" of the blank so it sits fine in the slot). Make the other side. Chop off the ends and there you go.

Actually the way I would do it is to have a bit made for the rail (client pays for it) and do it the way I show it on this topic.


Here is an easing that shows how it would look if you do it on it's side..


MAKING the opening cap could be on the indexer using normal methods.

Now the hole.......let me consult my fellow stair builders...I'm sure one of them can come up with something.

Could not resist messing with you Denver...please let me know if you need clarification or additional help...post or email me.


11-11-2008, 12:32 PM

The normal way to do this would be on a moulder for the straight section and a lathe for the round section, the straight piece would be bird's mouthed in to the round section. If you only have the Shopbot and have Partworks 3D you could do it with that.

I have just machined these (8" wide) with Partworks3D with 4 sided machining, I used a straight and ball nose bit with a 4 inch cut length. Drilling the hole you need separately will save some machining time.


Brady Watson
11-11-2008, 03:11 PM
You could have a shape cutter made & just do a profile pass around the outside perimeter...After you drilled the hole on the bottom & machined the top cap. If the inside corner has to be tight (no radius) then you can use a shape cutter as well, and machine a full 360 post topper, and miter it like Pac-Man via a saw and do the same for the main part so that they compliment each other when assembled. It all boils down to how many of these things you need to do. For a one-off, you can cheat a bit by doing a 4-sided setup as Paul has shown. Keep in mind that it will be time con$uming and not as clean as doing it with a purpose built shape cutter.


11-11-2008, 10:53 PM
this could also be cut from the side with the right profile bit. watched a video of a thermwood make curled ends all done with a side cutting router bit. http://www.youtube.com/watch?v=gdVzaAvsxMQ

11-12-2008, 06:59 PM
Thanks everyone, I know you could make the cap and rail separately using more typical tools, but for some reason they want this to be one piece. Not two pieces cleverly joined together. I also know that I can just drill the hole manually and get it pretty close, but I was hoping I could do the hole while the material is on the machine.



11-12-2008, 08:26 PM
I should add that they want just one of these.

Paul, could you tell me more about the ball nose with a 4" CEL? And how do you maintain an accurate position when cutting four sides? I've done fairly well with two sides by drilling locating holes at each end of the blank, and using the center as the zero point, rather than one corner. A four sided approach might be a good choice for this one.

Here's another image of the model:




11-13-2008, 07:35 AM

Can you give me an idea on how much time it took for the corbel (just cutting time)


11-13-2008, 08:10 AM
About 8 Hours in total. The 4" cutters only have 1" cut length plus a slow feed speed because of their length, the finish cut was done with only a 0.02 stepover.
Seeing the drawing in you last post the biggest issue will be the square internal corners. If I had Aspire when I did the keystones I could have isolated the cutting area and reduced the Z plunges to cut machinining time.
The cutter came from http://www.pacersys.co.uk/acatalog/Ball_Nose_Cutters.html in the uk.

11-14-2008, 08:25 PM
Thanks for the info Paul