Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Tim G-C on October 08, 2008, 05:27:20 AM
-
Hi Folks,
Firstly I hope this is posted in the correct section, if not .....sorry!!! :(
OK, My task is to convert (if possible) a Hegner HDB200XL ( http://hegner.co.uk/system/ ) wood lathe to CNC and Mach3. The linear slides, bearings etc are no problem. I am hoping to fit a rotary table style mechanism where the tool post would reside on a metal lathe to allow for undercutting of rims etc. I would also like to incorporate the use of a powered cutting tool e.g. Kress 1050.
I wand to be able to produce the standard range of goodies i.e. Hollow forms, Bowls Vases, Goblets, Platters, Pens, Furniture legs etc. etc. etc.
The thoughts bugging me at present are.
Is Mach Turn suitable for this task?
Does anybody here have any experience of such a conversion?
Can I have Manual Control at any time and if so how? As Wood is an organic product, right down to putting on the last coat of finish or whatever plans etc can change. Producing a CAD drawing and converting that drawing to a finished aluminium lump should be relatively straightforward, wood is a little different, hard spots, soft spots, voids, knots and even dormant bugs will be encountered. also what appears pleasing to the eye on a PC screen may not do so when the thing is sat in front of you. I would not want to have to write gazillions of lines of code to alter the sweep of a bowl rim but would prefer to take charge and finish it under manual control.
The initial idea was to run the ballscrew under the ways driving the 'Saddle' with the stepper tucked at one end away from most of the debris. However life would be a little difficult trying to turn a handwheel at the end of the lathe while trying to watch the cutting tip!! So any ideas on constructing the 'Saddle assembly' with a handwheel in the 'normal place' would be greatly welcomed.
Sorry its so long ...........
Thanks in advance.
Tim
-
With steppers and handwheels (manual handwheels that is) you would have to disconnect your motors physically or they would be hard to turn as they would produce electricity from your manual winding and would feel stiff and clunky.
You can however fit MPG's and use them as electronic hand wheels, I use them all the time on the lathe and mill but just usually for jogging on the lathe and occasionally for quick surfacing on the mill. Mine are just 100 line and have notches at each one so they are not the best if wanting to use them for electronic/manual style control. I have heard from quite a few guys that 500 line encoders used as MPG's work well and give much better feed control for manual milling/turning. Some people have some form of friction on them to give a bit of feel as well.
Hood
-
Hi,
Thanks for the prompt reply, I understand what you say in the physical sense but encoders??? mpg??? ??? Ah, you guessed it total and complete gibberish to my newbe ears.
Tim
ps now feverishly googling all sorts of stuff.
-
OK a MPG is a manual pulse generator, as you turn it it sends out pulses much like Mach does to the drives for your motors. Mach reads these pulses and dete\rmines the direction and speed of them and sends out pulses to your drives and your motors turn. In effect you have handwheels that have an electrical connection to your axis rather than a physical connection.
MPGs are just encoders but usually with less lines per rev, that means encoders casn be used in exactly the same manner as MPGs and are probably preferred when wishing to use them for manual machining rather than just jogging and positioning as I use them for.
Hood
-
OK, got that ... and yes, the way you put it, encoders would seem to be the way forward for the sort of thing I am looking for.
Thanks, that's one less thing to overcome.
Regards,
Tim
-
Tim,
I have no experience of a large wood lathe conversion but if you search this site, there are some examples. So, just a few general points. A big metalworking lathe might be a better starting point because all the precision slides are there already and they are not as expensive as a Hegner :) (Ask Hood if he has used his big lathe on wood.) You might be able to utilise just the leadscrews as driving elements, as neither absolute precision nor speed is the main aim with woodturning.
You will be surprised how few lines of code are needed to do turning in Mach3 and with wizards, which are like subroutines or canned cycles, doing a lot of the writing for you, it will not take you long to get used to how it is done. It will be a great timesaver in hogging out a bowl or doing a barelytwist with a router on the saddle. Manual input on something like this is better left to be done on another machine where you can do the finishing, polishing, etc. Interrupting a Mach cycle to do manual work might give you a few problems!
Steppers and servos are pretty dust proof but control boxes and computers usually have cooling fans to suck in the dust, so this has to be a consideration.
Hope this helps rather than confuses!
Regards,
Ian
-
Thanks Ian,
I admit you do have a valid point re the big metal lathe but I already have the Hegner and the credit crunch has taken hold of my wallet!! Even more so since I managed to trash my wrist, which, even with the Orthopods plates and screws has failed to return to any form of usefull mobility.
Dust extraction is not a problem, I have a very efficient system (I did a lot of flat work with MDF a while ago).
I may have to re think the whole idea as I now realise Mach may not take to kindly to halting a cycle. I can feel a 'thinking night' coming on.
Tim
-
No problems doing a feed hold and jogging away under most circumstances or at least I have never had issues that way.
As for a metal lathe I dont think that would be a good idea. Metal lathes are designed with long close fitting saddles that rely on an oil film for lubrication, wood dust will get in there and clog everything up.
I once got pestered so much by the boat yard that I eventually relented and did some oak plugs for them on a colchester lathe. The mess was unbelievable, dust got everywhere and clogged every slide and soaked up the oil. I had to partially strip it down to get the majority out and even after 4 yrs when I moved workshop I still found some under the saddle. The next time they came in and asked if I would l do some wood for them, I said yes no problem let me quote, 3 hrs to turn the wood and 1 week to totally strip down, clean and rebuild my lathe, they dont ask much nowadays ;D
One other thing about a metal lathe is the spindle speeds are probably on the low side for wood.
Hood
-
Tim,
Check out the posts on WHAT I MADE WITH MY CNC EQUIPMENT in here . There is a guy who is making some really
super turnings and I am sure he would have some good advice he would share with you.
Like Hood say's ball screws, linear slides and grease brings visions of binding. Not good. Acme screws may actualy be better. For any electrical device like a computer, controller, etc. i would recommend tight sealing and positive pressure / sweep so that you are not sucking dusty air in. Think about the tooling you will use as there are diferences in overhang /mounting, depth, width, and shape of the tooling you will use. Assume that you want the bull work done along with copying so that only fine finishing by hand will be done, so you want to be able to get the tool and slide out of way. Trying to mimic a knife cut / not scrapping cut and your into maybe 3D stuff .
STOP for a long moment and think about what safety you want in place when doing say a wooden queen ann leg. Ask yourself what are the differences that i am dealing with verses a metal lathe.
Just some thoughts,
RICH
PS: Buy a good mask as some of the exotics are really nasty and you don't want to find our the hard way that your allegic to the wood.
-
Cheers Hood .... ;)
Now I don't know which way is up!! (The joys of a knowledgeable forum)
I am going to proceed with the Mk1 plan and keep the lathe. Work out what electricial goodies I will need ... 3 Steppers, Drivers for the motors, PC, the encoders you mentioned . . . . . . . . . . . .any idea on what size motors?? I do not wish to be underpowered.
Oh just one small silly question (then I promise I shall go away) How does one control the Lathe spindle speed??? Hegner is a 1hp 3phase with variable speed over 3 ranges (belt and 3 pulleys) 70 - 3800rpm, plus reverse all running off 240v 13a
T
-
S[indle control depends entirely on what you want. By the sounds of it the spindle is controlled by a VFD so you could find out what input it takes to control the speed and get one of the boards that will output that signal when Mach tells it to. ie it may need 0-10v input to the VFD to vary the speed, some are 0-5v etc.
However you may not even wish to control the speed from Mach, nothing to stop you keeping it the way it is now and just manually adjusting the speed.
Motor size I am not sure on, depends on the forces required to move the axis, would think 916oz/in would be plenty especially if you gear them 2:1.
When looking for encoders make sure they are ttl.
Hood
-
Tim,
No way am I an expert manual woodturner but this picture shows some of the pots that I have produced. The biggest is about 125mm tall and all were made on a 3 in 1 manual lathe. All curves are circular with the toolpost bolted to an arm extension on a rotary table fixed to the lathe bed. The tool shown is about 10mm square and the top rake was generated with a 10mm diameter mounted point grinder. A Mach version would not need the rotary table and would allow for more varied profiles and it might get made someday.
As an example of CNC woodturning, how about a baseball bat in 1 1/2 minutes!
http://uk.youtube.com/watch?v=ov3awRWfVJc
Ian