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Author Topic: 9 X 20 Lathe project  (Read 2493 times)
dave benson
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« Reply #15 on: July 11, 2017, 06:04:53 am »

Another small update on the lathe project.
I removed the quick change gearbox and lead screw support bracket, and then cleaned up the surfaces (they were pretty good really).
With a bit of spare 12 mm al stock, I made a backing plate to hang the Z axis Lead screw on.
At first I mounted the Backing plate so that it did not run up against the saddle keepers and locking mechanism.(about 7 mm down from the bottom of the lathe bed).

Then changed my mind and milled a rebate in the backing plate about 10 mm x 550 mm to provide clearance for the saddle clamps, which meant that the backing plate was fully supported on 3 sides on ground surfaces. (I'm glad I did this as the plate became a very solid base on which to mount the Z axis lead screw)
Once satisfied with that, I  drilled and pined the backing plate and proceeded with mounting the lead screw support brackets.

I mounted the lead screw but found that even without being connected to the saddle yet it was
a little firm to rotate, smooth but firmer that the quality ones I'm used to work with.
I took the captured end bearing block apart and found that the machined end of the lead screw abruptly ended with no place for the seal to run on, and so the seal was running on the screw thread.

Thus providing no effective seal at all and because of the mismatch in diameter between the lead screw thread dia and seal expected dia, the friction was greatly increased.

So I removed the inner seal and presto the major cause of the friction was gone.
I intend to use enclosed lead screw covers so the missing seal won't matter.

I've seen a few of these conversions on you tube and wondered why Z axis motor was so big  (nema34's) usually.
I didn't have torque wrench small enough to measure the static and dynamic friction on the shaft
so resorted to an indirect method whereby I affixed a “corded” cordless drill to a power supply
and measured the current draw whilst tinkering with lead screw alignment.

I measured 2.3 amps to overcome the static friction and 1.93 for the dynamic friction at full speed of the drill. About 30 watts just to move the saddle.

Based on this (not very scientific method) I selected a Nema 24 (4nm 570 oz/in motor).

I also looked at a spreadsheet from here http://www.mycncuk.com/threads/1524-What-size-stepper-motor-do-I-need  check if my calculations were in the ball park.

IT said that I should get about 900 mm a minute at 180 rpm with a corner speed of 849 rpm.
With a 61 volt supply and a requirement of "2.788 nm" at full speed cutting.
I'm going to order one tomorrow  so time will tell if it's a poor choice or not!.
edit added  pic
Dave




* Lathe preparing surfaces.png (293.91 KB, 500x281 - viewed 52 times.)

* First fit up no rebate.png (294.63 KB, 500x281 - viewed 52 times.)

* Testing for motor requirements using current draw method.png (317.65 KB, 500x281 - viewed 61 times.)

* Lathe shot of rebate and pinining of backing plate.png (325.2 KB, 500x281 - viewed 51 times.)
« Last Edit: July 11, 2017, 10:31:40 am by dave benson » Logged
dave benson
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« Reply #16 on: July 14, 2017, 10:46:21 am »

HI All
A little information on getting the NVEM controller to work well.

While waiting on the stepper motor for the Z axis to arrive I started to set up the stepper drives for the project.
I will use two MA860H's to drive the steppers, I find these drives quite good to work with.

I first set up the MA860H/n series drive with no problems with Mach3 and the controller.

I then went to set up the older MA860H Drive for the x axis and then ran into a (missing steps issue).

After a bit of Noodling about I realized it was the drive not being able to process the 2.5 us pulse width.

So I replaced the step input optocoupler  (An 6n137) with a much faster 6n138 and I also socketed it while I was at it.
There's no point replacing the direction optocoupler and left it as it was.

Dave

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dave benson
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« Reply #17 on: July 18, 2017, 13:14:54 pm »

Another small update.
The stepper motor arrived today, I also ordered a 400 mm ballscrew for the X axis which I'll have to cut to size to suit the cross slide.

I  bench tested the motor at 24 volts and 3.2 amps set on the driver, at 1600 steps per revolution.
I set Mach3 to 1500 mm minute and a acceleration of 200 mm\s\s. (recommended settings)

Even with these quite modest settings I physically could not stall the motor, even at it's fastest feed-rate.
I then installed a grease nipple in the ballscrew and set about installing it properly.

I pulled apart the captured end bearing block and had a look at the bearings, nothing special just a couple of deep grove 6001 z's, It was then I realised that I could re-install the seal as there was a spacer missing on the one I received so I made up a new one 12x15x8.

Also the end cap socket head cap screws that held the bearings captive were unreasonably tight
even so  I detected a 0.06 mm end float and so installed a shim which fixed the problem.

I then made up some gussets for the 60 x 100 x 6 Al bracket holding the captive bearing block
to stiffen it up under cutting forces. They made a huge difference and I may keep the bracket rather than replace it with a 12 mm thick one as I was going to.

With the present feedrate it takes 16 seconds to traverse the bed (400 mm) should be 500 however with the 3 jaw chuck mounted and a live centre in the tail-stock that's about all you get.

Dave
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dave benson
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« Reply #18 on: July 24, 2017, 01:40:07 am »

Another small update
After spending perhaps 2 days on fitting the Lead screw (Had it on and off the lathe many times)
it's now moving very free and operating at the maximum feed and speeds that the calculations
said it should.

The captured end bearing block bracket had to be removed (it wasn't exactly at 90 degrees)
so I had to measure the angle 89.6 deg instead of 90 deg which doesn't sound much, however when you have a 600 mm lead screw attached to it and wish to capture the support end bearing this became several mm and had to be fixed.

I faced the bracket with the shaper (love that thing, as I only had to set up and do this once).
I've loc tighted the shcs that don't have to be removed (still have get some from the engineering supply tomorrow).

I set Mach3 up in mill mode and used a wizard to create a cut circle gcode, which swept the full length of the bed , the effect of this is to operate through all of the Accelerations and feeds from 0 to maximum.

Lastly as the code was running I grabbed onto the tool-post and tried to stop the movement of the saddle, not a chance even with the modest current settings I was using.

So far I'm very happy with the Inverter/3ph motor combination and now with the stepper motor for the Z axis, and would recommend them to other users with this lathe.

The X axis lead screw is on it's way, so for now I have to “sit on my hands and wait” which is killing me really as I'm excited to see it run now.

Dave


* Running at Maximun Feeds and Speeds.png (1207.88 KB, 1000x563 - viewed 57 times.)

* Installed and running free.png (2160.81 KB, 844x1500 - viewed 45 times.)
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dave benson
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« Reply #19 on: August 10, 2017, 02:54:45 am »

HI all

Another small update on the lathe.
I mirrored the topslide mounting spigot holes and reversed the gib from one side to the other.
And then after seeing the condition of the dove tails had to scrape them into some form of serviceability.
Unbelievably instead of cleaning up the raised edges from machining the dove tails they instead ran a angle grinder down the length of the underside of the topslide.
Anyway it's been scraped and runs smoothly and I've added some covers for the lead screw and am now waiting for the control box and another 425 oz/in stepper motor and a separate power supply for the controller.
I had to modify the splash plate at the back a little so as to get good air flow to the motor.

Dave


* dove tails full length shot pretty rubbish.png (1159.35 KB, 1000x750 - viewed 44 times.)

* dove tails after first round of scraping.png (1113.3 KB, 1000x750 - viewed 46 times.)

* cross slide set up and working smoothly Finally.png (1126.94 KB, 563x1000 - viewed 37 times.)
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dave benson
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« Reply #20 on: August 10, 2017, 02:56:32 am »

Here's a shot of the angle grinder fix Shocked
Dave

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dave benson
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« Reply #21 on: August 17, 2017, 11:49:40 am »

HI All
Well the control cabinet and power supplies came a few days ago, and I started to make some standoffs out of 25 mm round bar and piloted the holes with a 5 mm drill and then drilled them out to 19 mm by 75 mm deep and got through 7 of them when I had to stop as the motor was getting hot (pushing it too hard i guess).

So I let it cool down and went to squared up some 200 x 180 hot rolled plate on the shaper but he motor made a grumbling sound and started in reverse(it's a very old centrifugal starter type not a cap start).

I needed to get the work done so I popped down to the local engineering supplies and looked at a couple of motors Teco and a cheaper brand also made by them about 30 dolars difference between them. and after a bit of thought I opted for the severe duty inverter rated 4 pole 2 hp one just to be safe.

So I"m going to put the new motor on the lathe and swap the motor from the lathe to the shaper where it can run at full speed, the shaper has a 3 speed gearbox and a clutch and so should be happy.

The new motor is 30 kg's compared to the 11 kg's of the one I have on the lathe now, but the foot mount is larger and so I have to make another adjustable motor mount.

I'll post some pics when done.

I've tested the 425 oz/in motor for the X axis and it's working fine and with the 5mm pitch ballscrew, it's pretty zippy.

Dave

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dave benson
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« Reply #22 on: August 20, 2017, 13:56:25 pm »

Another small update

Today I fitted the new motor to a new motor mount and modified the belt guard to suit, I also modified the Splash Tray at the back of the lathe and will fit it as soon as the paint dries.

I also tested the motor torque by finishing of the rest of the motor standoffs for another project 13 of 14 mm holes 75 deep in al. unsurprisingly it did the job and stayed cool for the whole run, which took not quite 80 minutes.

Through the next week I'll wire up the control box cannibalising some parts from a control box taken from another machine bought at auction some years ago. I may need to buy a new stop switch as the one on the donor box looks a bit suspect.
Dave


* back view of new motor.png (1074.56 KB, 1000x563 - viewed 36 times.)

* new motor guard fitted.png (1058.36 KB, 1000x563 - viewed 33 times.)

* testing motor torque Drill 14 mm by 75 mm deep by 13 of each.png (1272.62 KB, 1000x563 - viewed 47 times.)
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dave benson
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« Reply #23 on: August 27, 2017, 13:12:15 pm »

Another small update.

The splash guard is fitted and the control box is finished and mounted.

I've added a emergency stop wire that runs the length of the lathe (so it can be stopped no matter where you are standing).
I've made some programs with Ezilathe and the mach3 turn wizards. including some rigid tapping ones.

I've also added a fan to positively charge the control box and unmounted the surface mount ethernet soccket from the controller and installed a ip67 enternet plug to the outside of the box and so won't have any dust issues.

I've picked up a large format vga monitor and a usb keyboard so that the netbook can be kept in a safe place out of harms way. and will modify the netbook stand to suit.

The only other thing I plan to do is make a tool holding block for the saddle, so that I can do some chucking work.

Dave


* control box wired up full spindle control.png (3374.46 KB, 1000x1778 - viewed 35 times.)
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Bubba
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« Reply #24 on: August 27, 2017, 13:18:46 pm »

It looks like you are making good progress. Are you going to do some threading on this lathe?
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dave benson
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« Reply #25 on: August 27, 2017, 13:36:27 pm »

HI Bubba

Yes I've already made some programs to do inside and outside threading with a tool in the toolpost and also some to do rigid tapping with a tap in a tool holder that I'll make in the coming weeks.

I've seen a young fellow on youtube make a tool turret for six tools and when I get the time, intend to make one along the same lines.

Dave
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dave benson
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« Reply #26 on: September 03, 2017, 10:32:55 am »

Another small update.

Well I ran the lathe for the last couple of hours, getting used to the Mach3 and Eazilathe turn wizards and produced a
few threads and faced and turned some scraps I had in the scrap bin, and am impressed with the threads now that I've got the hang of the setup for the lathe and software.

Of course I had a few scary moments, didn't have any home positions set, and the tool took of to the tool change position, which was towards the chuck Shocked but luckily have not broken any tools (I only had one threading tool).

I started off with pretty modest spindle speeds and axis feeds and the first thread could have done with faster spindle speeds to get a better surface finish see below, I also fritz-ed the chamfer tying to do it in the MDI.
The only thing to do now is clean up the area and sort the tooling out.

I'm going to have a break now for a couple of weeks and then look at a rear tool post and then make a six tool turret
like the one I saw on youtube that a young fellow made, which would give a lot of flexibility to the Lathe.

Dave
 


* First thread on Lathe.png (1205.13 KB, 1000x563 - viewed 35 times.)
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dave benson
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« Reply #27 on: September 17, 2017, 14:28:44 pm »

Hi All
Another small update, It's taken a lot of noodling and the odd expletive to finally get the lathe to thread satisfactorily
to my expectations. But I"m happy now Grin.

I did get a MachDrives breakout board to get the spindle  to perform accurately (It's got a 32 bit micro-controller just for this purpose) and works very well.

I've got some 8 mm carbide tooling coming  with a better threading tool holder (I just used a hand ground piece of HSS)
which I could have done a better job of grinding.

Dave


* m16 thread.png (2893.35 KB, 1000x1778 - viewed 26 times.)
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dave benson
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« Reply #28 on: September 17, 2017, 14:33:47 pm »

OPPs over the attachment limit
here's the other shot of the shaft.


* m16 and m12 threads.png (1150.36 KB, 1000x563 - viewed 29 times.)
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dave benson
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« Reply #29 on: September 19, 2017, 14:00:27 pm »

HI All
Have to make a correction I've ordered 12 mm tools not 8 mm.
Here's one last shot of a thread 1/2 inch 13 on the cut off end, of a 1/2 inch 13 rolled bolt.
Magnified X 10.
Dave


* 1-2 inch rolled thread on one end 1-2 inch turned thread on other end.png (1154.98 KB, 1000x750 - viewed 16 times.)

* 1-2 inch by 13 rolled end of bolt.jpg (138.71 KB, 1280x1024 - viewed 17 times.)

* my 1-2 inch by 13 on other end of bolt.jpg (126.45 KB, 1280x1024 - viewed 14 times.)
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