Thanks - that is good to know - 100IPM is 2540mm/min - so 15s end to end of the X-travel (the table is 840mm but the travel is ~600mm).Originally Posted by mwood3
The WM18 is a fair bit heavier than the BF20 IIRC - it's 260kg/500lbs and I'll have ~100kg/220lbs on the table with just 2 vices and a couple of decent chunks of stock.
I think beefy NEMA34's @ >=48v sound like a good place to start, and I can always go servo later if needs be.
NEMA 34 steppers will be fine. I run my mill with a 27kg 6" vice on one end of the table sometimes. When machining at the other end that puts quite a bit of friction into the system - absolutely no problems even at rapid, and that is on my low power system (39VDC @ 6A/motor).
Thanks - I'm sure you're right - NEMA34's will be fine, I tend to go a little speed crazy when I'm speccing things up - I hate slow machines as much as slow computers!
Not sure about breakout boards though - I think I might just recycle my EMC2 setup for now, though the 7i43 is looking interesting.
Well, I had hoped to get some work done on this, but my ballscrews got stuck in the snow, and then my car blew up:
which is going to cost me a lot of time and eat into my CNC budget.
But anyway, I decided to get going on the mechanical side: I have decided to go with 20mm screws all round, so I bought a spare sadle with the intention of modifying it:
I need to drop the axis of the ballscrew a few mm, so I decided to take 3mm off with a 40mm face-mill:
Cast iron is very nice to machine - once you get the inserts in properly - I bought that facemill at a show, and the inserts were in back to front, and so walked out as soon as I tried to cut with them! Worked like a charm once that was sorted.
This looked promising, so I took the bearing mounts off the X-axis, removed the X-screw and did a trial fit. Unfortunately the flange of the ball-nut still interfered
So I reassembled the mill and took another 3mm off - some of the casting was only 5-6mm thick, so I ended up with more of a cut-out than I had intended:
But the ballscrew now fits under the table
There's only 0.7mm of clearance at the top with the bottom of the screw 1mm above the casting.
Not too sure how I'm going to mount it - the bottom of the flange is inline with the original mounting holes. I guess I'm going to have to bolt it vertically though the centre of the saddle. I'll do some CAD before I get cutting again.
Damn, sorry to see that - doughnuts in the car park on the ice?
Hopefully the rigidity of the saddle won't be too badly compromised by the machining. That's a lot of material removed.
LongRat
www.fulloption.co.uk
Maybe I'm not seeing this right, but it looks to me like you've machined away a whole lot of metal you kinda needed to properly support the ballnut mount, which will likely totally offset whatever (small) benefit you might have gotten from using such a large screw. The ballscrew and ballnut mounts often ends up being the limiting factor on performance, not the screws and nuts themselves. It looks to me like you would've been much better off going with a smaller ballscrew, and not removing so much meat from the saddle, so you could provide a more secure mounting, without having to do so much structural damage to the saddle.
Regards,
Ray L.
Nope, straightline, part throttle, 4000 rpm and bang! At least if I'd being doing doughnuts like a halfwit, I could have crashed engine first into something and claimed on the insurance!
It's about 6mm all the way along, and 15.5mm in one web. There really isn't that much material in the centre of this casting anyway. I am thinking about milling the underside of the pocket in the casting flat, and then bolting on a reinforcement plate.Hopefully the rigidity of the saddle won't be too badly compromised by the machining. That's a lot of material removed.
What I am not looking forward to is boring out the nut-mounts to 36mm. My mini-lathe is too puny to take much of an unbalanced load - I guess I'll have to do it on my rotary table, or see if I can get decent results with a MT2-boring head in a MT3-adaptor. It'd take a lot of passes with the boring head though. Big holes IMHO are one of the best reasons to go CNC!
I managed to make a start on the X and Y nut holders. You really do take things for granted once you've used CNC - making 37mm diameter deep holes in metal is one of them!
I started off by squaring up a block of 80x50x50mm steel for the X-nut. Then I touched off it with my edge finder to set the datum on my DRO.
Then I started the holes for the ballnut fixing bolts and the ballnut body:
I'm using a spot(ting)-drill rather than a centre drill - notice the absence of an easy to snap off 'nipple' like you find on a centre-drill.
Then I drilled the bolt holes out to 5mm, and then opened up the centre hole with a 1/2" then 16 and finally 18mm drill. I have reduced shank drills up to 25mm but I don't really think the machine is up to it, unfortunately.
Then I mounted it in a 4-jaw on my mini-lathe:
After the big mill, the mini-lathe is frustratingly flimsy. I spent a couple of hours stripping it down and rebuilding it to try and address the twist in the saddle as the boring bar engages the steel. Got it pretty tight and smooth in the end, but I really want a bigger lathe!
Once it was all setup, the boring op went pretty well - I opened it up to 37mm odd.
So now I had the beginnings of a mount for the X-screw. The screw is way too high though.
So back on the mill it went and I took 15mm out of that block of steel. I still need to take one or two off the saddle where the mount will go and I'm also going to mill the back-side of the saddle flat so that I can re-enforce it with a steel plate.
Unfortunately I have taken out my low-range plastic gear again - that's the 3rd time and they're about £40/$60 a pop. Time for a belt-drive I think...
Blown the gears again?!
Was that by trying the 25mm drill in steel? I can't imagine how hard you would need to push this machine to smash those gears. In fact, I still am not sure that mine aren't all steel. Are yours black or white?
LongRat
www.fulloption.co.uk
I have tried drilling up at about 20mm before - even with the gibs locked, the torque seemed to want to make the table move a bit - and that was with largeish pilot holes of 16+mm. Perhaps my gibs aren't quite adjusted properly, but there didn't seem to be much torque at sensibly low rpm either...
No, I blew the gears face milling 35mm wide/0.25mm deep - which it usually doesn't mind, but for some reason it hung up, stalled out and stripped teeth
My gears are made of nasty green plastic - it's this one in the gearbox :
(from a previous failure)
- the spindle gears are metal:
Since I bought that replacement gear from Amadeal, I'm guessing you've got some plastic in there too...
I'm quite happy to accept that this is user error, but considering how well this thing cuts, I'm surprised it's so easy to take out the gears with a little abuse.
You must be unlucky. I didn't get my machine from Amadeal though, it came from TMTT.
I sent a 32mm face mill vertically down into a hardened vice jaw and it did not damage the gears. Just machined the jaw and smashed the inserts before I pounded the E-stop!
LongRat
www.fulloption.co.uk
Sorry - thought yours came from Amadeal.
I suppose you could have an all metal gear-setup, have you ever had the head apart to have a look? Looking at the real Opti-BF30, it seems to have a 3-speed oil-filled gearbox and 1.5kW motor so I guess there are quite a few variants about.
I also think it's probably more user error than luck - I've not cut much steel before, and was probably treating it too much like milling aluminium.
I think I'm going to have a crack at a belt conversion - I'm just not sure I can gear the stock motor down enough without a huge pulley on the spindle given its 55m OD.
Yeah I'll be keeping tabs on your spindle mods. I haven't stripped mine right apart to confirm the construction so I am assuming it is identical to yours until I know otherwise.
LongRat
www.fulloption.co.uk
I've had to be rather gentle without a low-range gear, but my X-nut mount is done, apart from some deburring.
Most of the work was actually getting it to clear the underside of the table - I will have to update the CAD with the revised measurements.
I think I'm also going to add a stiffening plate to the underside of the saddle - every little helps...
Wow, hadn't planned to pause for 4 months!
I finally got round to ordering a huge (600x400x250mm) electrical enclosure to put all the stepper drivers I've had since January into:
PSU's and stepper drives up one end
Mini-ITX motherboard, CF drive at the other
The mechanicals are getting there - but all the photos I've taken are horribly blurry
Both the X and Y ballscrews are on their temporary mounts - once I've got it bootstrapped, I'll CNC some proper ones on the machine itself
That's one big enclosure alright. What power supply are you going to run on those stepper drives?
LongRat
www.fulloption.co.uk
There are 2 70v 5A supplies mounted on one end of the enclosure - next to the stepper drives.
I plan to get a 4th drive if the performance of the first 3 is OK - two drives per PSU should be OK, I reckon. There's plenty of room for a 1kW toroidal supply if not
BTW LongRat - did you lose any Y-travel with your screws? My WM18's castings have a solid bar at the back that prevents the screw going through the hole in the column, and this also collides with the ballnut when the saddle is about 10-15mm away from the column...
I'll have to take and post some proper pics to show what I mean.
You won't be short of power then, I'm running only a bit over half the voltage that you are and I have had good performance now for hundreds and hundreds of hours of machining.
I did not lose travel with the ball screw, I actually gained with the conversion - removing the Z axis bellows and running off the front of the base casting a little more, if I remember correctly I have at least 238mm of Y axis travel. I don't see how you could lose travel, the ball screw is the same size as the stock screw it replaced and the nut is hidden under the saddle so can't interfere with things... I don't think. It has been a while since I was under there!
LongRat
www.fulloption.co.uk
The heads of the capscrews I'm using to secure the Y-axis nut seem to impact the casting at the back, but I suspect you're right - I've probably forgotten that the saddle didn't go all the way back anyway as it would have hit the way covers...
I think this should move pretty well - I had to lap in my Y-axis because it was very, very tight in places. I'm just waiting for some nice but rather pricey taper-lock pulleys to arrive as I've decided to go for belt drives on the Y and Z to give me more flexibity with motor placement.
I can't wait to see this thing moving under computer control - it'll just be 2-axis for now, as I'm not sure I've got the patience to hand make the part I need for the Z-axis screw - my biggest drill is 25mm and I need a 38mm hole for the ballnut.
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