cube inside a cube

[barnesrickw]

Thanks for the tutorial. I'm always looking for a project to do in the shop.

 

[bazmak]

I have made my second cube,40mm x 4.Slightly different method,quicker and easier.Milled ,chamfered and centre drilled.Held in the 4 jaw as previous and
machined the largest cbore to size on all 6 sides.
Held in a 3 jaw as previous and machined the 2nd cbore to all 6 sides
Finished the smallest cbore with a 12mm milling cutter to all 6 sides
With the carriage stop set for depth and using the dials its quick and easy
Dims are within 2 thou And concentric to about 3 thou.Havent yet separated
A woodruff cutter or int threading tool would do but i will probably grind down
a small boring bar for the inner ones and a slightly larger one for the bigger
cbores.This one took about 3 hrs.They get easier and like GREMLINS will
keep multiplying.Any thoughts on variations.O for CNC

 

[xpylonracer]

In the Digital Machinist article the cubes were intended to be cut by a milling machine and the tool recommended for the final parting cut was a 45 degree dovetail cutter. In the lathe the parting cut can be made by a suitably shaped boring tool.
Emgee

 

[Buchanan]

Brian S
You asked what cutters I use, A 10mm diameter and 32mm long cutting edge wood router bit and a 21mm diameter 2mm thick woodruf cutter.

I have attached photos of the cutters and also the tool paths I use.

There are three basic operations. 1 The rough bock is held in a vise and the top and halfway down the four sides are machined in one setting with the 10 mm cutter. The block is then flipped and the same operation is repeated. this gives you a totally square block with the first two stepped holes machined. This is done on the end grain faces. The second tool path is used to machine the other four stepped holes on the 4 side faces. Then finally the woodruf cutter is used to cut the under cuts. A vise with an end stop is used and the jaws are the height of the block for support. I forgot to mention that I drill a 10 mm hole through the center of the block from each side after the first operation. Two stepped plugs are needed for the last four cuts to support the
center blocks especially on the last cut when they are separated. I glue small pads of elastic band onto the plugs to give a little resilience an clamping and the fact that you are clamping on end grain also helps. This is for a 65 mm timber block. I modified the G code until they worked in pine and then made the proper blocks in Brazilian walnut. You may notice that the under cut tool path is square ,not round, this gives a better look to the inside of each block.
A hard close grain wood is best. the G codes have been fine tuned over about 16 blocks so far so they are reasonably good and the mill used is a small table top Chinese mill so the cuts are conservative. Total machine time is about an hour. If anybody is really interested I would pass on my G code. Just PM me.

 

[Buchanan]

Here are photos of the second tool path omitted in the last post as well as photos of the plugs and the machine used. The vacuum cleaner sucks the dust through the bottom of the vice.

 

[BrianS]

Excellent! I was figuring that you used a cutter like that but I was unsure. Now, I know... Thanks for the info.

 

[Smithy]

I have seen one recently completed using stainless steel (304 grade) - looks neat

 

[Cogsy]

I had to have a go at least, so I tried the techniques from the video.

First thing, the ring to hold the cube concentric has to be reasonably thick walled. I used a piece of tube/pipe I had that was the right size but it obviously distorted so my initial 3 through holes were off centre. This meant I had to increase the through bore and my inside cube is spider-web thin. Once I realised I just changed to the 4 jaw and it was very quick to set up each side to within a thou. I don't know why I avoid using the 4 jaw when I don't have it mounted, then once I am forced to use it, it generally stays mounted on the lathe for months.

Secondly, I used the hot glue method and it held just fine. Then I submerged the cube in freshly boiled water to soften the glue - big mistake! The glue turned all the way back to molten. I got the majority out but now I have spots of glue all over the place inside the cube. Next time I'll use some of my new moldable thermoplastic that I know will release all in one lump.

So here's the cube, probably as finished as I will bother on this one, but I think I learned enough that the next will be much better. This one is 35mm outside, 22mm middle and 11mm inner.

 

[bazmak]

They do get better after the first.Try my method of centre drilling all 6 faces in the mill,then push into the 4 jaw and hold central with the tailstock centre,
nip up the jaws.Should be concentric to 3 thou which is good enough
Turn the larger recess to size on all 6 sides.Then you can grip in the 3 jaw
using the oside of the jaws.I made a bull nose centre to fit the tailstock and again cetralised in the chuck.Then machine the rest of the recesses to all 6 side.
I am currently playing about with mine will post when i find something helpfull
I took my 2nd one to poker night,its quite tactile to play with and as a card keep.Didnt bring me any luck but will persever

 

[bazmak]

Another cube,my last for this thread.2 simple setups using 3 jaw and 4 jaw chucks.Concentric to a couple of thou no dial gauge needed and speedy
This one i wanted as a poker card protector.Found it quite tactile so improved it
Took off the 8 corners so it now stands on edge,on faces and on corner
mill and centre drill.Centralise in 4 jaw and machine large recess,repeat on all 6 sides. I made a simple bull nose centre,the cube is then held in the 3 jaw and centred.Finish machine all other recesses and chamfer etc.Repeat for all 6 sides