Desktop CNC 'Thing' build (includes welding!)

[Wedg1e]

Excellent
We had a machine upgrade job at work that required a Siemens PLC to be programmed. Our collection of recent electronics graduates collectively failed to get to grips with the coding; luckily the customer wasn't stuck as we were pushing 2 years late on delivery.
In desperation I asked my son-in-law if he knew anyone, and when I outlined the job he asked what we were poncing about with PLCs for, a Raspberry Pi could do the job just as well.
Raspberry Pi? I asked, you mean the kid's toy that 5 year olds learn to program?
Yep, he replied.
Find a five year old, I instructed.
Sure enough, in under two hours the bulk of the code was written. We had to use an Arduino clone to read a resistive height sensor as the Pi has no provision for analogue input, the Arduino plugs into one of the USBs on the Pi.
The Pi was stacked with a 16-input card and an 8-relay output for the hardware (doors, scissor table etc.) and talks to the system electronics via RS232 (even in the 21st century ). I designed and 3D-printed a case to hold the whole shooting-match together (even has a fan to keep things cool).
Bloody useful things, these kids' toys

Had to make a little piggyback cradle for the Arduino and somewhere to fit the DIN rail mounts...

 

[Misterg]

When I reassembled everything, I noticed that the X axis ballscrew seemed to be bent - the ballscrew nut mount was flexing noticeably as the screw turned.

I took it out again and got it centred up in the lathe and while it had some runout, I didn't think it was that bad (something like 1mm runout over ~400mm). Nevertheless, it seemed to be causing a problem, so I decided to try and straighten it.

I set the lathe leadscrew to the same pitch as the ballscrew so I could run the DTI down the ballscrew thread and plotted the total runout along the length.




Sure enough it had a couple of kinks in it (a small one at about 40mm and a bigger one at 100 mm - both in the same plane):

I managed to get them out by leaning on the end of the ballscrew with it held in the lathe chuck next to the bent bit, and got it running reasonably true. When I put everything back together, the ***** thing was still running out.

To cut a long story short, I eventually traced the problem to the way that the thrust bearing was mounted on the ballscrew.

The bearing arrangement is similar to this one:




There's a couple of angular contact bearings (not the plain ones in the photo) with a short spacer either side. The end of the ballscrew is machined down (by the manufacturer) to take this assembly and it all gets clamped into place by a locking nut. What was happening was that the spacer was a bit of a sloppy fit, and rather than bearing evenly on the (small) machined shoulder, it was bearing only on one point (at the end of the ballscrew 'thread') - pressure from the nut being tightened being concentrated on one side of the ballscrew was forcing the ballscrew to bend.

Once I'd figured this out, it was easy to make a new spacer that was a tight fit on the end of the ballscrew (loctited in place for good measure) so that the clamping load would be transferred evenly to the ballscrew.




Runout with the original spacer:

Runout with the new spacer:

With everything squared up, and the spindle trammed, I was still measuring a bow in the plate used for the Y axis carriage: +/- 0.07mm in the worst points.

The X axis had been set up straight to the glass plate and I went around in circles for a while trying to decide whether it was the glass plate or the Y carriage that was out, and whether the Y guide rail mounting was pulling the carriage out of true, but removing the Y axis carriage completely and checking it with a straight edge confirmed that it was much less straight than my glass plate.

I didn't want to pull my nice new table out of true, so I would have to trust the machine to skim the Y carriage flat (I know NOTHING about CAM or CNC programming, so feeds & speeds were, at best, educated guesses):

Some short video snippets of the first, tentative cuts -

Taking the first 0.1mm off the Y carriage plate:

Another 0.1mm fully cleaned it up:



Flushed with success, I got it to drill and chamfer the matrix of fixturing holes as well:

I had to tap them all by hand though ...

 

[MattH]

Great work.

 

[Misterg]

Great work.

Thank you!

Right then, that spindle.

It was a bad choice.

When experimenting, trying to find cutting depths and feeds that worked, I became suspicious that something, somewhere wasn't right.

I went through the machine, looking for backlash, play or loose fasteners, but I couldn't find anything amiss - everything seemed tight. I then started clamping an indicator to various places to see how much they deflected and eventually found that firm hand pressure against the ER11 collet chuck would move it by ~0.1mm. The spindle body was only moving by ~0.01mm under the same pressure.

This led on to the discovery that the spindle bearings were a) weedy and b) wedged into the end cap with a rubber boot!



At this point, I should have cut my losses and found a different spindle. But I had a couple of spare angular contact bearings, and there seemed to be a lot of fresh air inside the front of the spindle housing...

I copied the the original design into F360:





And indeed, as it seemed, there was enough space to fit in some more substantial bearings.

The only way I could think of to locate them axially was by sandwiching the original circlip (or something in its groove) between the pair of angular contact bearings that I had:



I had a suitable chunk of aluminium already, so the only thing I would be wasting was my time...

I needed to get the ER11 chuck off the old spindle to get to the bearing. My word, it was on tight! I had to heat it and jack it off the shaft with a bolt through a nut held inside the ER11 collet nut. It was that tight that I stripped the threads of a normal M6 bolt and had to use a HT cap screw one instead.

The new housing was just turned up on my lathe



(I milled a locating slot in it using my toolpost spindle before cutting it off the stock)



I didn't have a thread cutting tool small enough to fit into the recess in the front of the housing to cut the external threads for the preload nut, so silver soldered a broken M4 tap (I make my own ) into a piece of bar and ground off all but one tooth - voila: a full form 0.7mm pitch thread cutting tool



It worked quite nicely!





I made the preload nut and did the internal threading with the same tool:





The new bits and the old bits side by side



New bits assembled to the armature



In a burst of groundless optimism, I anodised the new parts. All I had to do now was get that ***** ER11 chuck back on. I thought I might get away with being civilised - I heated the chuck and tried to press it onto the armature using my lathe tailstock. It didn't want to know at all. I eventually resorted to brute force, and twatted it back on with a hammer.


In the process of replacing the chuck, I managed to smash up the brushes (I found out when I tried to power it up. There was a bang and a flash and all the lights went out...) Spare brushes are available from China with 3-4 weeks shipping. As I'm impatient, I ordered something close and sanded them to fit. While I was in there, I made a brass sleeve to replace the rubber boot on the rear bearing.





Perhaps unsurprisingly, the collet chuck didn't run awfully true afterwards (maybe +/- 0.05mm). I had marked the orientation of the chuck wrt the shaft when I took them apart, but my marks were inside the motor when I put them back together, so I couldn't see them! (I don't know if it would have made much difference.)

Anyway, it wasn't coming apart again, so any improvement would need to be made with the spindle assembled. I started thinking about how to set it up in the lathe to be able to re-cut the ER collet taper and realised that if I could support the spindle housing, I could true up the collet taper with it running in its own bearings. My fixed steady was *just* big enough to go around the new preload nut,



With everything running true, I clamped the steady onto the spindle and re-cut the collet taper





The best I could get was +/- 0.01mm runout when measured on the shank of a tool clamped in the collet. (I don't have any 'before' measurements to compare it to.)

I had measured the stiffness (compliance??) of the spindle before I took it to bits, and while there was an improvement afterwards, it was not as much as I had hoped - I was measuring ~800 N/mm before and ~2,500 N/mm after (measured at the top of the collet chuck). The stiffness of the spindle body measured next to the chuck is ~6000 N/mm).

It is also very temperature sensitive - the bearings tighten up when cold, so I need to run the spindle for a few minutes to warm it up before trying to cut anything. (I probably shouldn't have used aluminium for the bearing housing)

I was hoping to be able to turn a sow's ear into a silk purse, but I think all I've achieved is to make a slightly better sow's ear.

Whatever... I'm running with it for the time being.

 

[slim_boy_fat]

Genius. That's all I can say...sheer genius.

 

[Misterg]

^There's a fine line between genius and insanity, apparently

When I'd stopped fiddling with the spindle, I could let it loose on making a front panel so I could finish the electrics:

The engraving took *forever* - if I went much faster than 50mm/min, the cheap ebay engraving bits would snap. Because I was using the hobby version of Fusion 360 to generate the code, the 'rapids' are limited to the same speed.

Cutting holes was better (caution - loud)

The end result was this:



After a bit of de-burring (I should have run a pass around it with a chamfer tool) I was very pleased with the outcome:



It was a pleasure to be able to build the panel up with everything fitting nicely where it should. (I'd been hoarding that Neutrik USB connector for years, just waiting for something to come up that needed it.)



Finally, wiring that I'm not ashamed of! (It's not as bad as it looks to work on - the heatsink, with the drivers attached, can be unscrewed and swung out of the way to give access.)





It even looked a bit christmassy without the lid on




It made an actual thing - a mount to hold the SD card reader behind the slot in the panel. (Machined out of a slab of laminate. Thanks to some bug in my CAM, it managed to make a rapid move through the bottom left hand corner and take a chunk out of it. All part of the learning curve... )







I decided that the controller looked better with handles on it (I could pretend that I wanted them to protect the switches, etc. but I was just being a tart.)



As it was a sunny day, I carried it outside to take a photo before I got it too dirty. It weighs about 45kg!





X axis travel is 330mm, Y 235mm and Z 114mm. X & Y seem perfectly reliable at 4m / min, Z at 3.6m/min.

I have cut some test pieces on it, but I'm still getting my head around CAM and learning how to use the machine. I'll post some video once I've had a chance to edit it a bit.

I still need to sort out the ends of the Y axis bellows.

 

[fizzy]

Awesome build - very interesting thanks for posting.
One thing I would have done differently is build up a fly cutter for levelling your table. I have even seen them fitted to tiny Proxxons.

 

[minimutly]

^There's a fine line between genius and insanity, apparently

When I'd stopped fiddling with the spindle, I could let it loose on making a front panel so I could finish the electrics:

The engraving took *forever* - if I went much faster than 50mm/min, the cheap ebay engraving bits would snap. Because I was using the hobby version of Fusion 360 to generate the code, the 'rapids' are limited to the same speed.

Cutting holes was better (caution - loud)

The end result was this:



After a bit of de-burring (I should have run a pass around it with a chamfer tool) I was very pleased with the outcome:



It was a pleasure to be able to build the panel up with everything fitting nicely where it should. (I'd been hoarding that Neutrik USB connector for years, just waiting for something to come up that needed it.)



Finally, wiring that I'm not ashamed of! (It's not as bad as it looks to work on - the heatsink, with the drivers attached, can be unscrewed and swung out of the way to give access.)





It even looked a bit christmassy without the lid on




It made an actual thing - a mount to hold the SD card reader behind the slot in the panel. (Machined out of a slab of laminate. Thanks to some bug in my CAM, it managed to make a rapid move through the bottom left hand corner and take a chunk out of it. All part of the learning curve... )







I decided that the controller looked better with handles on it (I could pretend that I wanted them to protect the switches, etc. but I was just being a tart.)



As it was a sunny day, I carried it outside to take a photo before I got it too dirty. It weighs about 45kg!





X axis travel is 330mm, Y 235mm and Z 114mm. X & Y seem perfectly reliable at 4m / min, Z at 3.6m/min.

I have cut some test pieces on it, but I'm still getting my head around CAM and learning how to use the machine. I'll post some video once I've had a chance to edit it a bit.

I still need to sort out the ends of the Y axis bellows.

You sir are a genius

 

[Dr.Al]

Fantastic build and thanks for posting all the details. I really enjoyed reading this.

 

[snotters64]

Very interesting build . Would like to see it running in anger . Do you have a YT channel ?

 

[Misterg]

Thank you!

Good timing! - I ran into problems with EMI that caused the interface to randomly reset when taking heavier cuts. It took a long time to resolve that (with an interlude for Christmas, etc.), but I now believe it has been cured. (I tried increasing the filtering on the interface board and screening all of the spindle wiring inside the control box, but it didn't make any difference. I eventually traced the cause to the tool probe wire picking up interference from the spindle motor - whether it reset or not depended on where the probe wire happened to have been left. Once I'd realised that the brush noise from the motor was the problem, I fitted a couple of chokes close to the motor which seems to have resolved the problem completely.)

I spend today videoing it cutting a couple of test pieces in aluminium and steel.

It's just finished uploading:

I was surprised how well it did on steel.

Got to think of something to make with it now!

 

[GRW]

This thread has forced me to face that I'm a fick, ignorant, talentless bodger without a clue - and clearly I'm a different (inferior) species altogether .

Colour me mind-bogglingly impressed

 

[pawsnizzy]

This thread has forced me to face that I'm a fick, ignorant, talentless bodger without a clue - and clearly I'm a different (inferior) species altogether .

Colour me mind-bogglingly impressed

But you are honest and possess integrity! Can I join your club?

 

[Cheesie]

Brilliant build

 

[Misterg]

As a post-script to this, I decided to do something about the spindle - Even after the modifications above, it was still much less stiff than the structure of the machine, meaning slower feeds and light cuts to avoid chatter. This was exaggerated because the tool stick-out was more than necessary due to the depth of bore behind the collet being limited by the motor shaft.

I was a bit puzzled as to why the modified spindle wasn't stiffer, but eventually realised that it was just a result of the ~80mm chuck overhang, the 120mm bearing spacing and a 10mm diameter shaft - it was all just too bendy.

I figured out a belt drive ER11 spindle, using the existing one purely as a motor.

The spindle housing would be a block of aluminium that would bolt directly to the Z axis. The original spindle would get a drive pulley instead of its collet chuck and be mounted above the new spindle to act as a drive motor. There was room for a double pulley to give a choice of ratios for a slower spindle speed (e.g. for steel).



I designed the spindle around a pair of 7003 angular contact bearings (available as a preloaded, matched set as spares for spindles on Aliexpress for ~£20 delivered). It's a pretty standard arrangement with the A/C bearings clamped face to face (DB) by a pair of locknuts on the inner races and clamped into the housing by the outer races:

The A/C bearings allow a 17mm shaft which should be at least 8X stiffer than the 10mm shaft. For the best stiffness, the spacing between the nose and tail bearings should be 3-3.5 times the bore diameter of the nose bearings (according to SKF). A normal, deep groove, bearing supports the tail of the spindle and takes the side load from the belt. This bearing is a floating fit in the housing so I put an O ring around it to try and discourage it from spinning the outer race.

For the drive, I'm using a Megadyne TB2 poly-vee belt (J section poly vee would have been OK, but I couldn't find any short belts.)
The spindle shaft was machined from 20mm diameter EN16T (the steps in making it are on the 'Stuff you have made today' thread - here).



I had three goes at fitting the A/C bearings onto the spindle. Eventually, after scrupulously cleaning everything and warming the bearings to ~60°C, they slipped into place with moderate hand pressure. The runout on the collet taper was almost undetectable until the clamping nuts were tightened, then it went up to ~3µm. After various attempts, I couldn't eliminate this.

The housing was machined out of a block of 6063 aluminium.

Squared up using the milling slide on the lathe (this is absolutely the biggest part that I can mill!)



Then bored out to suit:



And anodised (with a bit of engraved bling )



The pulleys were machined using a form tool to give the 2mm pitch / 60° grooves for the PT2 belt - the stepped pulleys give either 1:1 or 2.5:1 ratio with the same centre spacing / belt length.



I anodised the pulleys and a few other bits together which resulted in the front clamp ring coming out an odd gold colour - I presume that this is because I've mixed different alloys up in the same run, but not really sure - the bath also got a bit warm which has caused some odd results previously...



Anyway, once the bearings were on the spindle it went together very nicely:





(I quite like the gold - just wish i knew how / why it had happened!)

I used the existing spindle to cut a couple of mounting clamps



and slotted them using a slitting saw, since I already had the vertical slide on the lathe




A bit more anodising:



This was the second go at the mounting clamp (the first one worked out perfectly as designed, but some eejit hadn't allowed enough clearance between the old spindle and the Z axis stepper - longer belt and new mount required ).

Getting the ER11 collet off the old spindle again turned out to be a real battle. Many bolts stripped or broken when attempting to pull it off. Heat didn't make any difference until I turned the TIG torch onto it, when it eventually gave up.

It wasn't pretty!



Luckily, the shaft could be cleaned up. I reversed the bearing mods that I'd previously made to the old spindle and fitted some new, standard bearings.






There doesn't seem to be any measurable difference in stiffness between the spindle and the machine. The runout is also much less than the old one - I'm measuring about 4µm on the tool shank with decent collets. I'm hoping that chips don't get stuck in the belt, but I can make a guard if it's a problem.

From the small amount of machining that I've done since fitting it, it seems to be a vast improvement - it's much quieter, too.

I'll post some video of it cutting once I have some.

 

[fizzy]

As a post-script to this, I decided to do something about the spindle - Even after the modifications above, it was still much less stiff than the structure of the machine, meaning slower feeds and light cuts to avoid chatter. This was exaggerated because the tool stick-out was more than necessary due to the depth of bore behind the collet being limited by the motor shaft.

I was a bit puzzled as to why the modified spindle wasn't stiffer, but eventually realised that it was just a result of the ~80mm chuck overhang, the 120mm bearing spacing and a 10mm diameter shaft - it was all just too bendy.

I figured out a belt drive ER11 spindle, using the existing one purely as a motor.

The spindle housing would be a block of aluminium that would bolt directly to the Z axis. The original spindle would get a drive pulley instead of its collet chuck and be mounted above the new spindle to act as a drive motor. There was room for a double pulley to give a choice of ratios for a slower spindle speed (e.g. for steel).



I designed the spindle around a pair of 7003 angular contact bearings (available as a preloaded, matched set as spares for spindles on Aliexpress for ~£20 delivered). It's a pretty standard arrangement with the A/C bearings clamped face to face (DB) by a pair of locknuts on the inner races and clamped into the housing by the outer races:

The A/C bearings allow a 17mm shaft which should be at least 8X stiffer than the 10mm shaft. For the best stiffness, the spacing between the nose and tail bearings should be 3-3.5 times the bore diameter of the nose bearings (according to SKF). A normal, deep groove, bearing supports the tail of the spindle and takes the side load from the belt. This bearing is a floating fit in the housing so I put an O ring around it to try and discourage it from spinning the outer race.

For the drive, I'm using a Megadyne TB2 poly-vee belt (J section poly vee would have been OK, but I couldn't find any short belts.)
The spindle shaft was machined from 20mm diameter EN16T (the steps in making it are on the 'Stuff you have made today' thread - here).



I had three goes at fitting the A/C bearings onto the spindle. Eventually, after scrupulously cleaning everything and warming the bearings to ~60°C, they slipped into place with moderate hand pressure. The runout on the collet taper was almost undetectable until the clamping nuts were tightened, then it went up to ~3µm. After various attempts, I couldn't eliminate this.

The housing was machined out of a block of 6063 aluminium.

Squared up using the milling slide on the lathe (this is absolutely the biggest part that I can mill!)



Then bored out to suit:



And anodised (with a bit of engraved bling )



The pulleys were machined using a form tool to give the 2mm pitch / 60° grooves for the PT2 belt - the stepped pulleys give either 1:1 or 2.5:1 ratio with the same centre spacing / belt length.



I anodised the pulleys and a few other bits together which resulted in the front clamp ring coming out an odd gold colour - I presume that this is because I've mixed different alloys up in the same run, but not really sure - the bath also got a bit warm which has caused some odd results previously...



Anyway, once the bearings were on the spindle it went together very nicely:





(I quite like the gold - just wish i knew how / why it had happened!)

I used the existing spindle to cut a couple of mounting clamps



and slotted them using a slitting saw, since I already had the vertical slide on the lathe




A bit more anodising:



This was the second go at the mounting clamp (the first one worked out perfectly as designed, but some eejit hadn't allowed enough clearance between the old spindle and the Z axis stepper - longer belt and new mount required ).

Getting the ER11 collet off the old spindle again turned out to be a real battle. Many bolts stripped or broken when attempting to pull it off. Heat didn't make any difference until I turned the TIG torch onto it, when it eventually gave up.

It wasn't pretty!



Luckily, the shaft could be cleaned up. I reversed the bearing mods that I'd previously made to the old spindle and fitted some new, standard bearings.






There doesn't seem to be any measurable difference in stiffness between the spindle and the machine. The runout is also much less than the old one - I'm measuring about 4µm on the tool shank with decent collets. I'm hoping that chips don't get stuck in the belt, but I can make a guard if it's a problem.

From the small amount of machining that I've done since fitting it, it seems to be a vast improvement - it's much quieter, too.

I'll post some video of it cutting once I have some.

Stunning quality work!

 

[Misterg]

Stunning quality work!

I wouldn't go that far, but thank you VERY much

 

[daleyd]

You shouldn’t be so modest Andy - your ingenuity and attention to detail is amazing! Superb work.

 

[Misterg]

Cheers, Dale!

 

[Misterg]

I've finally got around to some video of the thing actually working.

Skip to 0:30 to go straight to the chips without the preamble: