Ancient Knee mill retrofit

**kong** · 05-27-2005, 02:49 PM

Following along the same path as many others, I have sold my router an bought a mill. It is a Zenith knee mill, which is made in the USA funnily enough! The thing is old, probably around 50 years, but it has been owned by a model engineer for a looooong time, and is in reasonable condition due to this.
I have only just managed to put the thing back together since getting from the drive into the garage, and still have to hook up the motor (via 3 phase VFD for variable speed control) and tighten everything down.
I think the next priority will be to give it a good clean up, and a new lick of paint - that green is nasty!

**Al_The_Man** · 05-27-2005, 02:57 PM

Ah yes, that takes me back to the days of steam driven CNC.

Al.

**RotarySMP** · 05-31-2005, 04:31 PM

Nice machine. Similar to my Deckel engraver. How are you planning to CNC it. Ball screws?

**kong** · 05-31-2005, 04:33 PM

Yep, I have been busy on ebay over the weekend, just bought 3 ballscrews which are brand new, old stock. Originally made for Denford CNC machines, they are precision ground. I have started to paint the thing, but there is nt really a lot I can do before the screws and bearings turn up

**Mcgyver** · 06-01-2005, 07:12 AM

that's a classic old machine. kinda a shame to paint & cnc it, a bit like putting nitros and metal flake on a great old healey

**kong** · 06-01-2005, 07:15 AM

The paint is not the original colour anyways. There is quite a lot of sivery-grey beneath the pieces I have removed (such as the belt covers) so I am not doing any real damage.
You are right about CNC'ing though, but needs must! It is the largest machine I could fit into the overcrowded garage.

**RotarySMP** · 06-01-2005, 02:54 PM

I take it the current Z lead screw is has a stationary nut in the base, and the screw is driven through a crown and pinion gear. (Same as the deckel). Have you given any thought to how you are going to CNC this axis? I would expect the right angle gears to have unacceptable back lash.

What color are you painting it?

**kong** · 06-02-2005, 12:27 PM

Hi Mark, I am paiting it bog-standard goose grey, so it will look nice once it is all done. Just the head and table left to paint, but that will be done once all the "extras" have been addd to them.

Yeah, the knee operated via a crown gear, but I will leave this alone and use the knee just for tool-changes. The mill has a sturdy quill, which the sliding portion is 4" diameter. It is currently operated on a small worm drive via the front handwheel, but this is well worn and will not be any good to CNC.
What I have in mind is the method used by the mill-drill fitters, so I will mount the ballscrew on the side of the head, and attatch to the base of the quill. Then I can spin the nut to move the screw and quill up/down.
The biggest problem I will have is deciding the best place to mount the ballnut in order to minimize any flexing of the screw-quill mounting plate. Should be easy enough to strengthen it though

**RotarySMP** · 06-03-2005, 05:34 AM

I didn't look hard enough and missed the huge green quill right at the front

This will make the conversion much easier.

Look forward to seeing final pictures.

**kong** · 06-03-2005, 01:21 PM

Ok, so my bearings finaly turned up today, and I managed to make a start on the bearing blocks for the X axis. These two cast iron blocks were already on the table, so just required boring to accept a pait of angular bearings on one end, and a pair of deep groove bearings on the other. A quick 5 minute boring job....oh wait, I forgot it took me around an hour to mount the things on the lathe first! Nevermind, just need to make the spacer for the AC bearings, and the bearing-block caps to hold the bearings in place.

**kong** · 06-05-2005, 02:12 PM

I managed to make the little spacers yesterday, and made a start on turning down the ballscrews. Wow, they were hard! Had to grind off all the hard surface before turning in the lathe. I did attempt to take a deep cut to get under the surface first though, but this was impossible with my setup. I suffered worn tips, shuddering and even a couple of sparks! Nevermind, got the x and y screws turned down now.
I made the y-axis bearing block today, using the existing block, I have just bolted a piece onto it, bored for the new bearings, and made a nice hat to keep it all locked up. Next job is to work out the best way to mount the ball nuts.....X is no problem, but the y will be a little more tricky since I have big nuts

and not a lot of room under the table.

**kong** · 06-07-2005, 10:11 AM

Here we go, I managed to cut the nuts down a fraction so they fit under the table, and using a slab of cast iron for the connecting block, it is all working nicely. I had to notch the knee slightly to get the full table travel, but I never removed any real "meat". There was a thin section (maybe 1/8" thick) which just seemed to function as a swarf guard, so I drilled a series of holes through, and it came away easily with a soft blow from the persuader.