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View Full Version : Fun with a rotab when your CNC and CAD impaired



dockrat
01-24-2009, 04:33 PM
Yesterdays project was to make a block and tackle system to lift my rotab off the table and onto the mill. Nothing spectacular but in lieu of Niel Jones’s thread questioning counturing on a rotab I thought I would post this project. All made out of stuff in the scrap bin.

The two pieces of plate that were going to be the cheek plates were clamped to the table close to center and then the long cuts were indicated to the X axis and then cut one at a time. Four different cuts at four different angles. After each cut the table was rotated to line up the next cut to the X axis. ( I used the lil laser edge finder that Tiffie put me on to to do the indicating…I love that thing. When the red dot runs straight down the line…your there) Sorry…no pic of cutting the straight lines.

Next I had to cut the radii…three of them. The plate had already been drilled inch for the axles and end bolts so to center the plate I just used a piece of inch drill rod held in the collet and run into the hole to hold the plate on center while I clamped it over rotab zero.

http://i253.photobucket.com/albums/hh67/Dockrat1/IMGP1186Medium.jpg

I then lined up the longitudinal cut with the Y axis and then moved the X axis out the radius of the arc to cut and then got ‘er done. ( I always add a couple of thou to this radius because I can always take off a bit with a file but have a hard time adding it back if I overcut) Rotab was then moved back to center and the next center held in place and clamped then cut as above. Same for the third arc.

http://i253.photobucket.com/albums/hh67/Dockrat1/IMGP1187Medium.jpg

Next step was to mount the table vertical with my 3 jaw mounted on it to cut the sheaves. Two2 inch ones and 2--1 1/8 inch..

http://i253.photobucket.com/albums/hh67/Dockrat1/IMGP1182Medium.jpg

Next I moved to the lathe to cut off and face the sheaves and make the spacers and bushings. The sheaves were bored out and the bushings turned to a press fit. I didn’t have any of those fancy preloadable bearings in my scrap bin or I would have used those.

http://i253.photobucket.com/albums/hh67/Dockrat1/IMGP1185Medium.jpg

Cont……..

dockrat
01-24-2009, 04:34 PM
The finished product all bolted together.

http://i253.photobucket.com/albums/hh67/Dockrat1/IMGP1188Medium.jpg

John Stevenson
01-24-2009, 04:43 PM
Oooooooo Looooooverley, be a shame to thread wire thru this.
Stick it on the mantle piece and nip down Harbour Fright and get a Chinese pressed steel one ;)

oldtiffie
01-24-2009, 07:49 PM
Very very nice job indeed DR - from start to finish. A very elegant and practical solution to a known problem.

Its about time that someone showed that a lot is both possible and practical with basic tools - and without CAD or CNC. I will be the first to admit that it may be better done in CNC - but not that CNC (or CAD) are the only way.

As and aside - and not as a hi-jack, as it is related, I have pretty well finished the math etc. to do that job of John Stevenson's (in the previous thread you mentioned) and will post it shortly.

The reason I say this is that it too can be done on a rotary table on the mill table - without any other "X"-"Y" tables etc.

Sorry for the diversion - now back to DockRat's post please.

dockrat
01-24-2009, 10:48 PM
Oooooooo Looooooverley, be a shame to thread wire thru this.
Stick it on the mantle piece and nip down Harbour Fright and get a Chinese pressed steel one ;)

Nope...no wire....1/2" double braid. This was made from scrap...if I bought it from Horror Fright it woulda cost me MONEY and I wouldn't be able to afford those kippers for breakfast :)

rmack898
01-25-2009, 12:14 AM
Really nice job, what was the material?

I just can't imagine kippers for breakfast, or any other meal for that matter:eek: , although my Grandmother might differ.

dockrat
01-26-2009, 03:25 PM
Really nice job, what was the material?

Sorry rmack.... I missed your query till now. Cheek plates were anodized aluminum. Sheaves were 6061 Aluminum. Axles and spacers out of drill rod and bushings were bronze. Since I first posted this I put an eye bolt in the ceiling in line with the front edge of my mill table and hung the tackle from it. The whole setup worked perfect. That 10" rotab is way too heavy to be lifting by hand all the time.

HSS
01-28-2009, 10:43 AM
So dockrat, have you broken your camera or just loaned it out. Otherwise I KNOW you would have posted pics of the final install. Just wondering........:D

Patrick

Your Old Dog
01-28-2009, 11:12 AM
Damn nice job. Wish I had the computer skills to pull that off. That's the kind of projects I'd like to be able to do with cnc, nothing fancier.

BTW, any man eats Kippers ought to be banned from the board :D

Bguns
01-28-2009, 06:38 PM
He did not use CNC.... :)

Just a Laser Pointer/Indicator to adjust Table, until Laser tracked Scribed Line...

derekm
01-29-2009, 02:23 PM
These blocks form a 4 fold purchase i.e. it reduces the load by a quarter. Lifting RTABS of 75lbs+ need a 4 fold purchase to provide adequate control. (so dockrat has it right)
Having tried with a 2 fold purchase and its just not controllable.

Remember you will need a strong point e.g. a tube stanchion etc. to take a round turn with the fall (the bit of the rope you pull) to ease the load down. Dont lower it hand over hand. (which dockrat has probably already got).