Building a CNC Lathe

[mightymig]

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

I don’t have many spot drills, I have stub drills I guess that could be changed about. I got a metric ton in an auction lot - if you’re ever after one or two specific sizes I can sort you out

 

[northwest]

I got a metric ton in an auction lot

Holy smoke! and thanks very much for the kind offer, I shall bear that in mind.

 

[northwest]

Posted this once, I hope it doesn't duplicate this one, anyhow the pulley for the spindle drive made an appearance:



the bore is 11MM who the hell puts an 11mm hole in anything? anyhow, into the four jaw and get it clocked in:



So hands up those of you who thought that was how to do it. I can be a bit brutal, but I'm not that bad,
Clocked in using the tenths clock:




19mm it ended up being and to my surprise the key is 6mm so I am going to have a think about that, here is a pic which includes the new belt, I couldn't remember ordering it so I was pleased when it was in the package with the pulley. Only snag is, the spindle has to come out to swap the belts, ah well, you cant have everything:

 

[northwest]

Main job of the day though was to get the mount for the X axis Motor sorted out. In the words of @Tinbasherdan this setup was "shonky". A toolmakers clamp holding the tailstock of the mill vice so I could hold the piece of plate


getting the hole for the bearings right (and I did too!):





trial fit up on the cross slide:



Then with the ballscrew in:



Very pleased, it is all spot on:



Time to set to with the boring head, plenty of scope to create scrap here:



It worked anyway:



AND it lined up too, I was pleasantly surprised:


All cobbled together, tomorrow I will make the mount for the Motor



Hopefully the pulleys will be here or everything will have to stop!

 

[Migmac]

You’ve been busy. Great thread by the way

 

[northwest]

I just want to say something for the newbies to all this.
I can remember clearly back in the day when I would see what were to me impossible feats and somewhat mystical solutions involving MATH. I would be the first person to admit Math is not my strong point. Adding up I am equally as fast as a calculator, I am not just saying this, mental arithmetic is something I am really good at. Sine tables and equations, leave it out do we need that stuff now? Well it turns out we do and I really flounder some days but there is a trick anyone can learn. It is called attention to detail or careful planning and measuring. That ballscrew didn't just appear in the right place by accident. I wrote everything down and then did it all again checking then checking again until I was absolutely certain that what I was marking out was right, double right. Then it all came together but it is only by being methodical and critical of your own work can you improve and get it right "close enough" just doesn't cut it.

 

[northwest]

You’ve been busy. Great thread by the way

Thank you . I really need the pulleys now though as the size will determine how I mount the Motor. Yes I know you can get all the sizes online, I much prefer to have the bits in front of me and lay them out, then I am absolutely sure about position and clearances.

 

[Migmac]

Thank you . I really need the pulleys now though as the size will determine how I mount the Motor. Yes I know you can get all the sizes online, I much prefer to have the bits in front of me and lay them out, then I am absolutely sure about position and clearances.

That’s the best way, at least then you are 100% sure

 

[northwest]

Bit more progress today, pushing the envelpe on the small boring head.I just didn't want to get the Wohlhaupter out so used the little Creuselgui and pushed it to the limit really. Firstly needed to make a big bit of ally a bit smaller so took to the bandsaw rather than be knee deep in chips:



It cut just lovely:



Then oto the milling table and make a big hole:



Then the boring head:



Can you tell what it is yet, can you:



It's definitely coming together now:



Hopefully the pulleys will be here Tomorrow/Monday and it shouldn't take much more machining to see it done, then organise everything for my trip out. All very secret Squirrel but I am starting to see light at the end of the tunnel now.

 

[northwest]

Well, made the bracket for the Servo/stepper X axis motor, or rather, I finished the Bit of bracket I started, There are lots of these available on ebay etc. but I wanted it this week not next month.



Pulleys had arrived from Simply Bearings. I always use them when possible because even though it is "free" postage, it is always 24 hour so next day usually:



Got as much out as possible using a drill, it doesn't throw the swarf everywhere.





Figured if I drilled right through and there was a big hole in the bottom any debris would fall out the bottom and not get jammed in the pulleys.

Then a fit up. I had drilled and tapped for the NEMA 23 format, fit perfect:


Then offered up in a few different ways and I will think through the permutations and choose the best one, at least I hope it will be:





I really must sort those hammers out too, I have a plan. No time though :-(

 

[northwest]

Time to fit the pulleys on properly, I was initially tempted with a 3mm grub screw but sanity prevailed and a 4mm was used on the small (16 tooth) servo pulley:



Then it was time to look at the ballscrew pulley. I decided to counterbore it and tap it 10x1mm and then screw it on AND fit a grub screw, I was able to grind a flat on the shaft just perfectly placed after a trial fit-up.



The counterboring and tapping operation went just fine:



The bottom bracket/cradle for the motor was modified to remove the sharp edges that might have caught on the belt:



Then the whole thing was fit up to the mounting plate. I am a bit disappointed with the fit to be honest I followed exactly the 81.4mm centre to centre distance and there is far too much slack in the belt:



I am not sure what to do next to be honest, I did consider slotting the bracket mount and just pushing it taught and bolting it up. An offset tensioning bearing would be a far more elegant solution but a quick check of the stores didn't produce a suitable bearing:


I would welcome suggestions at this point as it looks so good and went together so well I dont want to "spoil the ship for a haporth of tar" as it were

 

[Hood]

Slotted and push to tighten was the way I went.

 

[northwest]

Yes,I think this is probably the best option but I am soooo tempted to make a real fancy cam type tensioner in stainless. Simplest is always best so probably stick to plan A and slot the plate. At least there is plenty there for me to have a go at.

 

[m_c]

I've never seen anything else other than slotted on CNC machines.

If you want to get really accurate with tensioning, IIRC the Gates calculator gives the recommended frequency for the ping test, and I do have a belt tension frequency tester, although I have never used it on a CNC machine.
I had it for doing the old 1.9 Renault engine, as it had a manual tensioner that was set based on frequency.

 

[northwest]

I've never seen anything else other than slotted on CNC machines.

If you want to get really accurate with tensioning, IIRC the Gates calculator gives the recommended frequency for the ping test, and I do have a belt tension frequency tester, although I have never used it on a CNC machine.
I had it for doing the old 1.9 Renault engine, as it had a manual tensioner that was set based on frequency.

Simple problems I try to do elegant solutions but I went with Slotted and it's done. The belt and pulleys are High Torque Drive (HTD) and the profile reflects it, very deep.Even slack it's not going to slip, very pleased with it really. Anyhow just one job left and that's tomorrow, remove the spindle and install the new belt, the saddle and cross slide are done:



Sorry, I forgot, make a "nut" for the toolpost. First thing tomorrow:



Loads of clearance for the motor and it is well out of the way:




You can see where I slotted it for the mounting bolts, worked just fine:

 

[northwest]

Nuts, or rather nut:



It was pure chance a 17mm socket fit:

creating the hex:



I worked out 17.5 degrees was optimal:



Came out just lovely:



Looks the part n everything :-)

 

[Agroshield]

Even slack it's not going to slip...

Any slack in the belt is backlash in the system, which cancels the no-backlash of the ballscrew that it is driving.

You would only notice it if doing a profile operation like a handwheel handle where the cross slide has to go in and out as part of the same cut.

There would be some tolerance in the pulley and (rubber) belt manufacture, so the theoretical centre distance is just that and the manufacturer is doing no-one any favours quoting it to 0.1mm.

 

[northwest]

Any slack in the belt is backlash in the system, which cancels the no-backlash of the ballscrew that it is driving.

I hear you loud and clear but the point I was trying to make is that this belt/pulley profile is very much suited to this application and I will be using this HTD profile on my Clough 42 leadscrew conversion on the Harrison, it is a deep profile and High Torque Drive describes it well. What I am saying is it will not slip, under most any circumstance, getting it taut and removing any backlash a given really.

 

[northwest]

Nothing to add today, all ready for my journey to the far North, to the wastes of Scotsland, the Plains of the Picts. Time to gird my loins, paint my face with blue stripes and Sally Forth to the cry of "SZGH Controller" and "Servo Motor" at the top of our lungs, will report back later!

 

[northwest]

Well the journey was pretty uneventful, aside from the pretty spectacular scenery, it is all too easy to forget just how spectacularly beautiful our country really is:


Truly stunning and made the journey pass quickly (it wasn't it was five hours):



Then towards the very end of the journey the most spectacular copper beech hedges:



All beautifully maintained too. More later, suffice to say I am very confident this will work just fine now.