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Messages - John S

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11
General Mach Discussion / Re: Problems threading on the lathe
« on: April 09, 2009, 05:43:55 PM »
Pretty picture time.
Loaded the driver up Art posted and upped the acceleration as high as it would go and did the usual 50mm long 2mm pitch thread, 2 scratch cuts.



Slight tracking out from midway to the end, then cut this to full thread.



Not bad looking, crests are out even though the acceleration was right up but still off on pitch. Next run the 1.5mm pitch thread. This was also out



Didn't bother doing a full thread for this one,  so out of interest slowed the acceleration down.



Tracking better but the end is closed up due to the slowing down, went back to mid point on acceleration and started playing about with speed, so far these have all been done at 600rpm. Going up caused the pitch the get courser and it's already out, dropped down as low as 150 and started working back up.
the pitch of the thread was altering according to the speed.
This is the 2mm pitch at 300 rpm and that's the best one I have cut yet.



This is 2mm at 600 rpm, double tracking and to course on pitch.



One funny thing I have noticed is that the first cut makes one track, the second id off but subsequent passes want to follow the second pass as though the first pass is a settling path ?

John S.


12
General Mach Discussion / Re: Problems threading on the lathe
« on: April 08, 2009, 05:14:14 PM »
Got a chance to run some more tests on the lathe.

First Art asked if the averaging made any difference, with averaging off it moves between 615 and 595.
http://www.stevenson-engineers.co.uk/files/P1000649.MOV

With averaging on it's steady at 600 to 604
http://www.stevenson-engineers.co.uk/files/P1000650.MOV

Now scratch testing on alloy, fresh tool, machine cleaned and slides lubricated.
First test is 50mm long @ 2mm pitch



This is typical what I have been getting.

Next test was the other end again cut 50mm @ 1.5mm pitch which is what Steve usually tests with.



Now I have never had that before but Steve has, however mine looks cyclic in that it looks to be going on a wander at the 50mm end.

So dump the driver, reboot, install new driver, run driver test and reboot again.



Back to test 1, 50mm x 2mm and we get this.



Now that looks good so carry on and do a full thread. One thing I noticed as it was cutting was the chip load wasn't constant from pass to pass, one pass would take a sliver and the next pass would be a lot deeper. More disconcerting though was it would cut heavier in different parts of the thread.
One pss say at the start, another pass at the end and so on.

Finished thread.



Using a blued tap as a gauge, start looks good, nice crests but the end is ragged, thin crests and out of pitch. This is consistant with what I'm getting on 2mm pitch threads.

Back to test 2 with the 1.5mm pitch threads. Start again looks good.



Finished thread.



Good crests at the start but gets rough towards the end, pitch isn't bad but the tap doesn't want to sit in the threads anywhere, it rocks about as if the middle is right but the ends stop it sitting correctly.

This non compensated driver seems to be the best of the bunch so far.

Shout up if there is anything more I can do or try.

John S.

13
General Mach Discussion / Re: Problems threading on the lathe
« on: April 07, 2009, 08:31:33 PM »
First off a little background for the machine.
It's brand spank new and has been designed as a CNC from day one.
Spindle is driven by a 500 watt 3 phase brushless servo with encoder feedback to the driver board, this then drives thru a 3:1 timing belt reduction so it's at max torque at 800 rpm.
True speed at a requested 800 rpm is 800 to 804 and steady.



Ballscrews fitted with no discernable backlash, no compound, everything tight.

I'm running the same tests over and over which is a 2mm pitch thread 80 mm long, short threads don't show an error like the long ones and I'm positive that you need to cut long threads and use a tap or known screw as a pitch gauge because a thread gauge fits along the thread due to the fact it only covers about 4 or 5 pitches.

This is what I'm getting for the first three cuts




Unlike Steve who was getting a narrow land at the start and end and OK in the middle I always get a good thread at the start and an increased pitch at the end causing the land to become very narrow.
At the end of 80mm I'm about 1/2 a pitch or 1mm out.

Art has picked up on aluminium threads being OK but they were shorter ones for a job.
tomorrow, well later today as it's 1:30 am here I'll cut a long alloy thread with the same driver I have on the machine now.
Then I'll swap to the driver Art has sent and redo the threads in alloy and steel, scratch cuts at first.

John s.


14
Thank you Tweakie but in truth is all down to software, all I did was press the big green button.

John S.

15
Finally got the sign for my brothers dogs grave.

Name and layout done in VCarve, angel imported from a Dover clipart book



John S.

16
NC Pod / Re: status of NCPod
« on: November 01, 2008, 10:50:27 AM »
Why do you and Chaoticone ( apparently an administrator) plug the Smooth stepper rather than answer the OP's question.  Why don't you post in the smooth stepper topic area instead of the ncPOD?  Is the use and development of the ncPOD unwelcome here?

Possibly because the Smooth Stepper is a work in progress and it quite up to date.
Greg is addressing problems and the plug in is also being worked on.
Hood can't comment on the NC Pod as he doesn't have one.

I do and it has serious problems in locking up and I'm not the only person to have this.
Do a search on the Yahoo list to see.

I have tried many things to get by this, new computers [ 5 in all ] which all work on the parallel port, upgrading firmware and plug in's.
I even borrowed a NC Pod off John Prentice who has exactly the same problems and that was the same as mine.

There is no pattern to the hang up, can be just into a program or anywhere else, all you get is the Mach screen still running and a message at the bottom saying NC Pod has stopped responding.
Problem is you don't know where as Mach is still running so the job is scrap.
You have to reboot to get out of it.

It was a good idea but the support was never there for it, mine sits abandoned on the bench with John's at the side, he never even wanted his back...

I will shortly be working with the Smooth Stepper as I want it for a high speed threading lathe.

John S.

17
So I picked this lump of brass up today and thought "I wonder what's hiding inside this ?"

Threw an old Myford chuck on the bed of the trusty old KX1.1 and lobbed the brass in roughly on centre.

Bit of stabbing with a 6mm cutter got it to look like this.



Swapped to a 2mm ball nosed cutter and ran the intermediate file and sure enough this was hiding inside.




Ran the finishing file which does a cut at 90 degrees to the first and got this.



Still got a few tool marks but most will polish out with a bit of wet and dry.

Could have made it better with a less value step over of the finish tool but didn't want to waste a lot of time if it wasn't going to work.

Crap video of it doing one of the final cleanup passes here.

http://www.youtube.com/watch?v=RV8Dq6mslnE

John S.

18
Here's the V Carve screenshot for the plaque for my brothers dog that recently died.
Still waiting for the lump of oak to carve it on.



John S.

19
Just black paint in an aerosol, sprayed on and wiped off whilst tacky with solvent. The brass plate was cleaned up with fine wet and dry when the paint had dried, nothing fancy these were not jobs as such but demo pieces to put on the display stand that goes to shows with the various machines.

John S.

20
Don't really want to post my pic's as the router has been busy this week cutting circular gear blanks out of Tufnol [ phenolic] sheet 24 at a time
and when you have seen one washer you have seen it all  >:(

Got to do a plaque for my brothers dog this weekend but waiting for him to supply the material.

Only pic's to hand are these.



And this which was done in brass as a joke, it's the name of a village in Wales and this is a copy of the station sign.



.John S.

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