CNC conversion BL250G/700 lathe

[MrCrankyface]

Finally doing some real work and not just side-project'ing.

Cut off the rear handle, chopped the trigger into bits and mounted it underneath, adjusted by hand with a screw, new on/off switch mounted on the side where it felt natural.
A bit shoddy but just wanted to get it functional so I could move on.
Just some notes for the future:
1. Oscillating mass needs to be a lot less, especially at larger strokes it shakes a lot, which gets annoying when you work for several hours.
2. Total mass should preferably be less too, whilst it probably helps dampen the hits, it also gets quite heavy to hold after a few hours.
3. The undergrip is not very useful, I mostly, intuitively, want to put my hand ontop of it or on the front.


Despite the flaws it's still an insanely useful tool and makes it a joy to scrape.
Went at it on the saddle and since it's mostly flat from inking it on the granite plate, I next decided to try to match it to the lathe bedways after giving them a proper stoning.
Took a little bit for me to get comfortable but even the tiny V-ways were easy to work on, especially with the stroke down to just a few millimeters.
Still some ways to go but good enough for it to sit solidly.


Decided to move on up and match the crossslide to the saddle, even after a few passes this is the tiny inking I got on this side.
Took me >10 passes just get it in plane, there's faster ways but I need the practice.


Few hours of work and the coverage is looking pretty good.
There's some artifact that's scraping/smudging the ink on the top right(crossslide/master) which I need to figure out.
I also think I'm going to doublecheck the crossslide on the graniteplate since I've gotten a lot better at both scraping and inking things up.
I think the better my master is, the easier the sadle will be to get just right.

 

[MrCrankyface]

Took me all about 4 seconds before going off the rails into another side project.
Now that I'm more comfortable with scraping and powerscraping I want to sharpen my carbides to proper angles and radiuses.
It'd probably 'good enough' to do this by hand as I've previously done but a good jig would reduce errors and make things more repeatable/predictable.

Came up with this little jigg for R30, R40, R60 and R90.
The carbide holder has corresponding holes underneath.
The carbide is lightly pressed down into it's holder and the M8 screw is used to carefully advance it for grinding.


I have 240, 800 and 2000 grit diamond discs I was going to mount to the side of my tormek-clone, unfortunately it had some serious axle-wobble issues, making it unuseable for this.
Whipped up a quick wooden frame and printed some pieces.
The main shaft is 12mm rod ment for round linear ball bearings, very straight and consistent.
Then it's just 2 bearing blocks, some sprockets, mounts, disc clamps etc.
Incase the discs themself were slightly warped, I added a ball bearing behind where the grinding happens, should help support the disc.
The block the carbide-jigg is sitting on is removeable so I can use this for other purposes as well.


Rough grind with 240 grit and then 'polish' with 2000. Super quick, repeatable and easy.
This is R30 which I then took out and rounded the corners on, to lessen the chance of messing up the surfaces if I angle too far.


The idea is to also add a thing to the side so I can sharpen my sawblades/slitting saws.
The two 'rings' are 250mm and 216mm, the typical saw blades I use, but the jig should work for any size up to 300mm or so.
The bar protruding towards the two rings will index against a tooth to make sure each get ground the same.
Might need to make a carriage stop as well, won't really know until I make it and can get a feel for how it works.
I have a whole pile of slitting saws I need to sharpen so this would help a lot, but now back to working on the lathe now that my carbides are sharp and properly radiused.

 

[MrCrankyface]

Checked and did a few more passes on the cross-slide, now it has pretty good coverage even with extremely thin ink.

Which also let me finish off the saddle surfaces.
Far from perfect but good enough for me.


To start working on the dovetails I need to scrape in my camelback again, since I never fixed the angled surfaces..
It quickly annoyed me how hard it was to avoid chatter.. Granted that this is very close up, but should still not have all those chatter marks.
The machine is very sensitive to being held at the perfect angle and I suspect that my carbide isn't sharp enough.


So instead of carrying on, getting more and more frustrated I figured I should try to find the issue.
Tore the machine apart and cleaned some parts up, the tool holder could previously rotate/wiggle sideways a bit so I tightened that up for a stiffer mechanism.
I also made a new carbide holder from regular mild steel, much softer than the old one and also a bit longer.


I've only tested it for a few minutes on the workbench but it feels A LOT better. I tried provoking chatter by leaning the machine forwards, backwards etc and nothing seemed to cause it to bite, and the long soft shank seems to work much better to let you know how it's cutting and now much force you're applying.
The bench plates has machining marks so it's not a fair test but so far it seems a lot better.


Decided to go deeper into blade sharpness since I imagine a sharper blade is always going to be better at shaving off thin bits.
80-100x zoom-ish and things look OK-ish but the cutting edge is diffusing some light which makes me suspect it's not sharp.


Top of the blade, straight from the 2k diamond disc, much coarser than I would expect from such a high grit.
Bottom and front has been polished which helped a tiny bit.


Much higher zoom onto the cutting edge shows the full truth of tiny fractures everywhere along the blade.
I've ordered some diamond paste stuff and hoping that will be able to get a better finish after the rough shaping with my jigg.

 

[MrCrankyface]

Sometimes things just work out!
Finally got the diamond paste, flycut 3 alu pieces, first a finishing pass to get them flat and then a second shallow pass at high feedrate to create a kind of crosshatch pattern in the surface. Should help both retain the slurry and stop the carbide from getting sucked into the surface and get stuck.


I wasn't very thorough with each step as I just wanted to test if it would work or not, definitely A LOT better than before.
Previously I could just about 'guess' what it was mirroring, if I had it real close up to something, now it's almost as good as a real mirror.


Left is the old 'grind' and right is after the 3 steps of diamond paste.
Clear signs of not spending enough time on each step as both 20µ and 7µ scratches are visible.
More importantly, the entire edge now looks much more solid and well-defined.
I need to make some kind of mount to my slowspeed grinder so I can hone the 'front edge' but can't wait to give this a try!

 

[MrCrankyface]

Alright so that kind of sharpening did A LOT of difference.
Surface finish is way better and hardly needs stoning.
I also paused scraping the big camelback since it's going to be unwieldly on these small lathe parts.
Instead I made a smaller 'wedge' from some cast iron I had left over, good practice piece and should come in handy.


Overall shape of it. I just squared it up and milled the angled surface then started scraping.


3 hours-ish to reach ~30 ppi, very happy with how things are working at the moment.
I'm probably gonna give it a second stoning pass to see if I can increase the coverage % a bit, I imagine it'd help the ink transfer when used as a master.

 

[MrCrankyface]

Scraping dovetails.
So tedious and so much effort for so little progress.
Ah well.. Cleaned it up in the mill, the face was bent and twisted all sorts of directions, basically banana-shaped both length and heightwise.


A couple of passes in, quickly got contact on the outer sides which made inking it up a bit easier.


I'm just gonna call it here, wish it was more uniform but it's way too tedious and boring to work on to chase perfection.
Now to match it to the saddle dovetail, probably milling that first too.

 

[MrCrankyface]

Finally back on track, sortof. It's been a really fun and interesting side-project to scrape this in, learnt a ton.
Just by what I've learnt, I can tell that much of this scraping could use improvement, but it's also insanely much better than it used to be, so I'll go with it so I can make more progress.
With the cross slide scraped in, I matched the saddle dovetails to it for good contact and also scraped the gibb since it wasn't even near flat.
I can finally adjust it to have no detectable gap/play and still maintain the full travel without binding.


Next up is:
-Match and install the gibs that clamp the saddle to the bed.
-Make a toolholder to replace the compound and install this directly on the crosslide.
-Design/make a mount for the telescopic spring cover for the long ballscrew.
-Reinstall all the hardware and new oilpump
-Design/make the control box so I can test the hardware out, once tested I will remake all plastic parts in aluminum or steel.

 

[MrCrankyface]

Kinda feels like I'm back to where I was several weeks ago.
Getting the bottom-gibs in place was quite a lot of work but finally got it fixed and started re-installing everything else for further tests.


Tried to get a better shot of the bottom gibs/clamps.
I've milled them "short" and then adjust the play with shims.
Takes quite a while to insert shims, tighten everything, measure play, loosen, change shims, tighten, measure .......
And finally make proper shims that sit on the entire surface, but finally done.


Moving my todo-list over..
-Design/make a mount for the telescopic spring cover for the long ballscrew.
-install new oilpump
-Design/make the control box so I can test the hardware out, once tested I will remake all plastic parts in aluminum or steel.

 

[mattthemuppet2]

nice work!

Next time with gibs like that, make them thicker, slit them and use set screws to adjust fit. Kind of how Criterion boring heads adjust the dovetail. A little more time machining, much less time adjusting.

 

[MrCrankyface]

That actually sounds way better, might make some new ones eventually and just replace these stock ones. Thanks!