Building a CNC Lathe

[northwest]

There are flats, they are on one side of the spindle only though so I will mill a corresponding flat opposite and make sure I can get a good spanner across them.

 

[m_c]

IIRC it's the flat would have been for the grubscrew to hold the original pulleys onto the shaft.

I think I just used a set of molegrips to remove the chuck when I had one. Bit crude, but it worked, although I rarely had any reason to remove the chuck from mine.

Although it has reminded me, I reamed my spindle out so I could fit 16mm bar through it, instead of the stock 5/8" bore.

 

[Fastdruid]

One advantage of steppers over servos, the holding torque.

Probably would be enough to hold it in place while you undid it with a beefy enough stepper (just not otherwise ideal as a spindle drive).

 

[northwest]

Although it has reminded me, I reamed my spindle out so I could fit 16mm bar through it, instead of the stock 5/8" bore.

I might as well do this while it is out, I will just stick it in the Harrison and run something up through the bore.
Thanks for that.

 

[northwest]

I have decided t to a bit every single day, that way it will get done sooner rather than later, mounted the drives today and installed an on/off switch:

 

[northwest]

Well, here we are three years later and full steam ahead, this machine will work this month, properly, or it will be in the 'for sale' section! I have a very cunning plan, but not until I finish off all the mechanical bits. So yesterday I mounted the three phase closed loop stepper to the Z axis, it was not straightforward. I became quite disillusioned with this when the Chinaman didn't send me the servo and drive I had ordered so I just abandoned it. This has been a temporary setback as I am now full steam ahead once more, it is going on it's holidays in a fortnight (more on that later) so I want all the mechanical bits fitted and working properly.
First snag was a Nema 23 wasn't the same as the previous drive, not wanting to make a ridiculous adapter plate (the holes were only four or five mm out) I decided to fill the holes with ally bolts then re-drill and tap them. Snag was an ally bolt came in at £4.57 each. I discovered that Amazon sold 12" lengths of 6mm ally rod for a tenner delivered so I ordered some. In the lathe and a die down it produced threaded ally rod and a bit of Loktite secured it in the original holes:






There was something else and it was the other part of the Oldham coupling, not wanting to or needing to order a whole unit I just chucked up a bit of ally in the Harrison and set to.

 

[northwest]

This really was a "quick and dirty", half way through I realised the Mill vice wasn't bolted down, not to worry, it was square to itself!



I was in a bit of a rush so not too many pics I'm afraid:

Grub screw to retain it:



Bound to be one in here:



It's in there somewhere:



I fancy milling a slot in the housing then using the borescope to check it's mounted properly, or just trust my measurements.

Today's job, the cross slide. I am not happy with the way it is so I am going to explore mounting the drive on the back of the slide for compactness and clearance.

 

[northwest]

Okay, it all came to a screaming halt again and I welcome suggestions from the collective. As you can see from the photographs, I am trying to fit the Ballscrew and Drive to the cross slide, of course it is all a bit much:




If I am not careful I will have very limited for and aft movement and I want to be able to mount a parting tool upside down on the rear of the slide, for parting off obviously. It occurs to me that I don't need all that much movement as I am restricted by the swing of the lathe. The ballscrew itself passes through this hole that held the original cross slide screw. (well it does now after I drilled it through with a 12mm carbide bit!)






Pal of mine suggested angular bearings in a new thrust housing to steal another 15mm or so as the supplied housing is quite big? Maybe even 20mm:



I am going to have to come up with some sort of contrivance in order to mount the motor and hopefully I have enough room, I really don't want it out front as this would be something for me to walk into and god knows what I would break. It also takes up room that I could otherwise use.

 

[Agroshield]

The motor does not need to be co-axial to the ballscrew.

A couple of timing belt pulleys would allow it to be repositioned better.

Potentially, it could go below the ballscrew, with the wire end of the motor facing towards you. Especially if the ball screw sticks out the back a lot, it uses up the dead space below it.

If you only use a single tool, you need half as much movement as the maximum diameter the lathe will swing - so the tool can go from the outside to the centre. If you add a rear parting tool, I think the movement might need to double (!) or the rear tool will clash with the work.

Here is my reasoning: imagine something 2" diameter. The main tool needs to move 1" to go from stock OD to lathe centreline. When it is at the OD of the stock, the closest the parting tool can be is also be the OD of the stock, the other side of the centreline. To part the stock off, the rear tool also needs 1" of movement, so the axis needs a total of 2" of movement.

You are not going to want to hear this, but a smaller Nema-series stepper motor coupled with a belt reduction on the cross slide will save space and still have enough strength.

 

[Hood]

This is the way I did it.

If I recall I had the ball nut connected to the plate arrowed but then I had a very small ballscrew of 8mm if I recall.
I don't recall the exact setup of the bearings but I think it was just thrust ball bearings either side of a plate and tensioned by the pulley position, seemed to work well for the little I used it. The whole setup is now on the plasma and still working well with the exception of the ballscrew as I had to replace that as it got full of plasma muck and eventually died.

 

[m_c]

Could you mount the double bearing on the front side, so the back side only needs a single support bearing?
Then belt couple the motor, which would also reduce total length.

 

[northwest]

To be honest, on this length and the amount of movement it is going to have I wouldn't bother with a bearing on the end only at the motor end would I put a bearing. Yes, there are lots of 'but it will do XYZ' or the world will come to an end. I only need it to give me a couple years and then I can change it out for a new one or I won't be around to worry about it, one or the other.

Right, I need to get to it so will be back later.

 

[m_c]

The original setup on these didn't even use any bearings. They simply had the ballscrew rigidly coupled to the stepper motor, and relied on the motor bearings to control end float/backlash, so anything is likely to be an improvement.

 

[mightymig]

Off topic completely but how have you found the performance of that drill grinder? Is it the split point or thinned web version?

 

[northwest]

It started off well and I triple checked the vice was square:



Quite a bit of measuring went on then I got the biggest magic marker I could find to mark it with:



Exact comparison were made using the No. 1 eyeball device, Then I just went for it :-)



It came together:



and actually fit up. I had to cut the ballscrew housing to make it work. Clucking Bell are those things hard! I couldn't believe it, even running carbide flat out I destroyed a couple of 12mm solid carbide cutters. Forgot to take some "finished" photographs but it has been a long, hard, non stop day. I am totally bushed and painfully aware that I am not quite as young as I think I am. Not anymore I'm not anyhow.



And a gratuitous pic of the servo/stepper I am going to try to mount on the X axis:

 

[northwest]

The Law of Unintended Consequence

The translation of course is "you didn't think about this" and it's true, I didn't, or maybe I did but thought I could get away with it. Anyhow it caused a few moments of pukker that's for certain. When I slid the saddle on it was immediately apparent:



Now that ain't right. AND it rocked, yup! The Ball Nut was protruding below the saddle face, nothing else for it, going to have to machine the ballnut further. Now I am very aware as to how ballscrews work so My thoughts were "will I find the return channel?" Thankfully I didn't. I machined off 1.15mm




Back in the saddle, I was getting fed up with replacing the spring washers.



That's the top obviously but the bottom cleared:



All back fitting nice n snug:



Tomorrow I will make the frame up to carry the pulleys and the motor, well that's the plan, hopefully the new Spindle servo pulley will arrive and I can get it bored and reamed then get the keyway cut.

 

[northwest]

Off topic completely but how have you found the performance of that drill grinder? Is it the split point or thinned web version?

My apologies, I meant to reply yesterday, but I fell asleep! Anyhow, back in the room, I find the grinder excellent. It is especially useful to me for sharpening Carbide drills. Yes they are expensive but the drills are too. I seem to recall it is the split point version. I don't pay much attention, it just works.

 

[northwest]

Righto, on with the X axis drive today and because I needed to drill and tap the cross slide I discovered someone had dropped it:


The corner was damaged, careful use of a flat file quickly brought it back though.


Then I set it up in the Mill for a drilling and tapping session on the end.

Rightly or wrongly I have decided to do away with the "framework" style design an mount everything onto a piece of 20mm alloy plate, it should look quite funky. Ordered the pulleys and bet now I have settled on a design 32 tooth HTD 9mm wide belt at the top and 16 tooth on the motor end. Found a real nice calculator here:

Timing Belt Calculator - Belt Length Calculator | B&B Manufacturing

Calculate the length of your timing belt with B&B Manufacturing's belt length calculator. Stock and custom belts available.

www.bbman.com

 

[mightymig]

My apologies, I meant to reply yesterday, but I fell asleep! Anyhow, back in the room, I find the grinder excellent. It is especially useful to me for sharpening Carbide drills. Yes they are expensive but the drills are too. I seem to recall it is the split point version. I don't pay much attention, it just works.

Good to hear thanks! I was looking for the same reason, diamond wheel for the carbides. Good luck with the rest of the build

 

[northwest]

Good to hear thanks! I was looking for the same reason, diamond wheel for the carbides. Good luck with the rest of the build

I got it out specifically because I had chipped THREE Carbide Spot drills! And they ain't cheap.