Trying to learn… And looking for a CNC Lathe

[richardandtracyParticipant @richardandtracy]

I have been lurking as a guest for a couple of weeks & this is my first post. I would appreciate it if someone may be able to help me – possibly just to confirm that I am looking for the right thing.

As a hobby I make pens, and sell a few kit pens at the odd craft fair. My particular interest is fountain pens. The precision required is quite remarkable – add or subtract 0.1mm from the diameter & the whole feel of the pen changes.

At the moment I make them on a combination manual lathe/mill (the Warco version of the Clarke 500). This has adequate precision and repeatability, but it can take up to 13 hours to make the pen – an example of a 'proper' fountain pen can be seen on the front page of my web site http://www.chestnutpens.co.uk . Now, like most hobbyists I'm short on time, cash and (to a large extent) skill. However, like almost everyone, I want to do something extraordinary.

I have been thinking of what I want to do for some time, and it comes down to taking less time to make the pen, make curves more easily, and do engraving on the barrel of the pen, replicating gilloche or fancy shape knurling – as that will make the pen look absolutely extraordinary.

To the best of my belief, this needs X (to lathe axis), Z (along lathe axis) and C (rotation around Z axis) control. From the research I have done it appears there are no hobby machines like this.

Can I ask, am I correct that there are no hobby machines to do this?

I have found at least one industrial machine that will do it ( Daewoo Puma 1500Y), but at 5 tonnes, it's not a hobby machine, and probably takes more power than my entire village. I have also seen Bill Ooms site on his conversion of a Jet wood lathe to do a similar job ( **LINK**&nbsp, however I would strongly prefer not to convert a machine if I can avoid it.

I would greatly appreciate it f you would be kind enough to share your knowledge and advice on this subject.

Regards,

Richard.

[richardandtracyParticipant @richardandtracy]

[Another JohnSParticipant @anotherjohns]

Richard;

I'm describing a Unimat CNC conversion on my blog; maybe something like this would work?

The unimat I'm using is one of the originals, with shorter bed, and I have not put the tailstock back on it (yet)

Also, more to post this coming weekend (I hope) as I only work on this in the evenings after work and the chores are done.

http://cnc-for-model-engineers.blogspot.com

is the blog address.

Ask questions if the approach is of interest to you. Unimat lathes seem to come up for sale with regularity (there must have been millions made!) and the conversion can be quite inexpensive.

Another JohnS.

[Another JohnSParticipant @anotherjohns]

Maybe posting too quickly –

I think I mention in the blog about moving the spindle by cnc control.

My current CNC Unimat uses the original motor; phase 2 (pardon the "it's end of the work week" pun) is to put a stepper motor for spindle control for precise threading, etc, etc.

*then* the little lathe gets really interesting!

Another JohnS.

[BazyleParticipant @bazyle]

Is it not the fact that they are handmade that makes them special? The Chinese can knock out machine made ones for peanuts. Would it not be more interesting to make a rose negine to put on the decoration?

[richardandtracyParticipant @richardandtracy]

Bazyle, the fact they are handmade is nice, but there are a lot of things I want to try in the way of shape & decoration. My aim is to finish the pen (or even lots & lots of pens) within my skill level and use it/them rather than to spend years at the lathe creating a work of art to admire. It's the using, rather than the making, that's the object! With a manual lathe I am at the limit of my skill level and cannot really progress much further in the direction I want to go without the time to produce each pen rising exponentially.

Gaagh. Win 7 & IE 8 won't allow me to put in carriage returns in the editor – having to copy & paste from notepad. This is slightly irritating!

Regards,

Richard

[richardandtracyParticipant @richardandtracy]

John AS,

I shall take a look, thanks.

Regards,

Richard

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Richard ,

A couple of observations :

(1) Would it not be more interesting to make a rose negine to put on the decoration?

Bazyle makes a very valid point .

All the features that you want to reproduce on your pens can be done by purely mechanical means . Read up about ornamental turning lathes starting with the Holtzapfel –

**LINK**

and see some of the amazing work done by the Society of Ornamental Turners –

**LINK**

(2) A low cost CNC milling machine may be a better choice than a low cost CNC lathe .

When it comes to ornamental pattern forming even a cheap CNC milling machine fitted with fourth (rotary) axis will do almost anything that you can think of .

Regards ,

MikeW

Edited By MICHAEL WILLIAMS on 01/06/2013 08:29:59

[Sub MandrelParticipant @submandrel]

HI Richard,

I love fountain pens, but despite having had some very nice Parker and Waterman ones in the past I only have a feeble cheap Parker 'school pen' at the moment. You're website has made me want to make my own pen.

Where do I start! Can I skip the kit stage and go straight to my own materials (is wood practical? I have a block of yew I've been seasoninmg for about five or six years).

Neil

[richardandtracyParticipant @richardandtracy]

Neil,

There is a massive world of fountain pens, and the largest online community is the Fountain Pen Network at http://www.fountainpennetwork.com (FPN). I am a moderator there and go by the name 'richardandtracy' (same avatar), with particular responsibility for the 'Pen Turning and Making' forum. There you will see many pens made without kits.

You can go direct to kitless pens, but there are a surprising number of details that need to be bourne in mind at the same time. At the minimum you need a nib unit (which consists of a nib, finned feed to regulate the ink's flow and friction fit housing which is threaded on the outside and has a cartridge spigot already built in) and a cartridge convertor to hold the ink from a bottle and then machine everything else to suit. The best nib units available to custom pen makers come from Bock or JoWo in Germany (they also make nib units for almost all the Italian pen manufacturers and the remaining British ones such as Onoto and Conway Stewart). Unfortunately their minimum order quantity is very high, and the only UK based re-seller is John Sorowka (user name 'oxonian' on FPN) . Other re-sellers tend to be in the US, and you end up paying quite a bit more than from John. The nib unit needs to be put in a 'section' with a difficult thread (M7.4×0.5 for JoWo and something equally awkward for Bock). Then the section screws into the barrel. I use a 3/8 x 26 TPI BS Cycle thread, though it is a bit coarse. Then the barrel is shaped & the cap screw thread mates on the barrel. This thread has more flexibility, but is ideally a multi start thread. I have bought an M12x2.4 triple start thread tap & die from the US as my lathe is missing my preferred 3mm pitch gear wheels – and I have not yet suceeded in making an acceptable thread in anything using the lathe.

I would advocate that you do NOT try to make a nib. It is possible by brazing a ruthenium pellet to a gold substrate, then slitting the nib with a 0.001" saw, and finally grinding the tip, but it really isn't worth the effort. A really good stainless steel nib will cost less than £10.

As for using wood in a kitless pen, I have to say I wouldn't advocate it as the main material for your first pen – but later on, yes it's possible. The ink needs to be kept well away from the wood otherwise it will stain. To prevent this you need to use a lining inside all the areas that may come into contact with the ink, preferably with a plastic that can be threaded for the critically loaded threads between the cap/barrel and section/barrel. Delrin is a good plastic to use, but acrylic or a good pipemaking hard rubber can be used too. A note about hard rubber. It is a surprisingly good & durable pen material. The oldest pen in my collection dates to about 1915 and is perfectly usable (infact I use it every few weeks), having a body of black hard rubber and a gold nib.

Metal pens are heavy, and almost all metals corrode to some extent when in contact with inks. Even modern inks (which are less corrosive than old ones) can vary from Ph 2.1 to 9.5 depending on the maker & colour. That is why it's a good idea to have a plastic liner in contact with the ink – like a nib unit mentioned above. Otherwise, try your first pen from alumium or brass. The chances are you'll have some in stock, and first pens always have areas that could be improved so it's not sensible to make your first pen from some precious material be it wood, silver or gold!

Through sheer bloodymindedness I do not use a nib unit. I machine my sections so that the nib and feed friction fit inside the machined plastic section (the bore needs to be different depending on section shape and stiffness and may vary between 6.1 and 6.3mm for a nominally 6mm diameter feed). Then I also machine a 2.5mm diameter spigot on the other side of a bulkhead with a 1.5mm diameter hole through the middle so that this forms the spigot required for a cartridge. The tool I use is a very simple home made silver steel rose cutter, though I hope to get and end mill with a 2.5mm hole in the end made soon, as my rose cutter melts the plastic if I cut more than 0.05mm between applications of coolant (melting at 80C) – and the spigot length is 3mm, so 60 cuts are required. I cannot use external coolant to any effect as the plastics insulate very well, and there is no room to cool from the inside.

I hope that looking at some of the amazing pens on FPN will inspire you,

Regards,

Richard

[Sub MandrelParticipant @submandrel]

Thanks Richard,

That's a fascinating, if whistle-stop, tour of pen making. You might want to think of extending ita little, adding pictures and submitting it to Model Engineer? I can't be the only reader interested in such things.

Neil

[richardandtracyParticipant @richardandtracy]

You're joking, right?

I know model engineers have all the correct equipment & skills.

Hmm, maybe. It would be different, and I suppose it is rather like the idea of clock making. Clocks aren't models, but they do feature fairly often in ME, require loads of applicable skills and create a usable result.

Oh dear. I may have another job.

Regards,

Richard

[maurice bennieParticipant @mauricebennie99556]

Hi , I have used pen kits from AXMINSTER TOOLS . every thing supplied but the holder, which can be made of anything .I know this is cheating ,but I am not clever enough to do what you are trying .

The kits are good ,I think they are from U.S.A. and use a standard roller type ink cartridge also a pencil version.

best wishes Maurice.

[richardandtracyParticipant @richardandtracy]

Posted by John Alexander Stewart on 31/05/2013 20:47:39:

Richard;

I'm describing a Unimat CNC conversion on my blog; maybe something like this would work?

The unimat I'm using is one of the originals, with shorter bed, and I have not put the tailstock back on it (yet)

Also, more to post this coming weekend (I hope) as I only work on this in the evenings after work and the chores are done.

http://cnc-for-model-engineers.blogspot.com

is the blog address.

Ask questions if the approach is of interest to you. Unimat lathes seem to come up for sale with regularity (there must have been millions made!) and the conversion can be quite inexpensive.

Another JohnS.

 

John,

I have at last had time to read your blog. Fascinating. Thanks for pointing me to it.

I am coming round to the idea of converting a lathe – well, at least I know a bit more and can now get a handle on how much I don't know (to use the immortal words of Donald Rumsfeldt the 'Unknown Unknowns' are becoming 'Known Unknowns' and may eventually become 'Known Knowns'  ) . If I convert a lathe it will probably be a Clarke CL430, as it's basically the lathe part of my machine and all tooling will be common between the two – saving a good deal. I notice you use the NEMA size 11 motors & have had a couple of issues with stalling them – I suspect the saddle of the Clarke will have much more inertia. After testing my Warco, a NEMA 23 should be adequate for the cutting forces and static friction, but I'm wondering if the inertia factor may not mean that the next size up would be better. To be honest, I'd rather spend a bit more on the motors & have something that's over powered than inadequately powered.

Regards,

Richard

 

Edited By Richard Williams 7 on 03/06/2013 11:14:44

[richardandtracyParticipant @richardandtracy]

Maurice,

I too use kits from Axminster tools (as well as other suppliers). They have a shop a mile up the road from me and it's very hard to resist popping in. I never use ball point pens, but a lot of people do, so I make ball point kit pens as well as rollerballs. Strangely enough, pencils don't seem popular.

The Axminster 'Empress' and 'Chairman' pens have fountain pen variants and use a pretty good nib, but I always swap them out for a JoWo nib in the width they want before passing the pen on to someone who has asked for one. Basically, I don't want to let anyone use one of the pens I've made unless I'd be happy to use it myself.

I've also tried nib grinding to make italic nibs, and have got to the skill level where I'm happy to use one of my italic nibs – but I'm not yet happy enough to let anyone else use one yet, they are still a bit crisp and scratchy if not held at the perfect angle. I need to practise more.

Regards,

Richard

[BazyleParticipant @bazyle]

It's a bit like lace bobbin making. There is a whole world of interesting activities out there with an engineering/modelling aspect that we know little about. My club once had an interesting talk on air brushes – from a couple of cake decorators.

[John Stevenson 1Participant @johnstevenson1]

Posted by Richard Williams 7 on 03/06/2013 11:14:07:

After testing my Warco, a NEMA 23 should be adequate for the cutting forces and static friction, but I'm wondering if the inertia factor may not mean that the next size up would be better. To be honest, I'd rather spend a bit more on the motors & have something that's over powered than inadequately powered.

Regards,

Richard

Richard, type 23's are fine, go for 180 Nm on the cross slide and 3 Nm on leadscrew geared 2:1 reduction.

No need to go bigger in fact it can be a disadvantage as steppers have most power at zero speed, called holding torque and you have to overcome this.

The bigger the stepper the greater the force needed.

It's a common fallacy that bigger motors are better when in fact they can actually hold you back.

Best advantage for a stepper is speed which is derived from the voltage. I know a guy who's converted a Lux mill with type 34 steppers on it at 1600 oz/in. It's embarrassing to watch it machining where many short line moves are needed. It never gets close to it's programmed feed rate.

[Another JohnSParticipant @anotherjohns]

Posted by Richard Williams 7 on 03/06/2013 11:14:07:

I have at last had time to read your blog. Fascinating. Thanks for pointing me to it.

…. If I convert a lathe it will probably be a Clarke CL430, as it's basically the lathe part of my machine and all tooling will be common between the two – saving a good deal. I notice you use the NEMA size 11 motors & have had a couple of issues with stalling them – I suspect the saddle of the Clarke will have much more inertia. After testing my Warco, a NEMA 23 should be adequate for the cutting forces and static friction,

As John Stevenson mentions (and, he has experience that puts me in the dust, to use another americanism!) NEMA 23 size motors would be what I would choose for a larger lathe.

I'm learning as I go, as are many others here.

BTW – I think the steppers are going to be fine, now that I have some issues fixed – hopefully I'll get it finished up in the next few evenings, and then I can see how well (or not) this little lathe works!

After that, I have an Emco Compact-8 to convert. That will be a very good, strong lathe for CNC working.

Another JohnS

[richardandtracyParticipant @richardandtracy]

Posted by John Stevenson on 03/06/2013 20:48:57:

Richard, type 23's are fine, go for 180 Nm on the cross slide and 3 Nm on leadscrew geared 2:1 reduction.

…

John,

Was that 180 oz.in rather than N.m? I must admit my eyes boggled a bit at 180 N.m torque from a motor that small. I've not seen one more powerful than 4N.m. After a couple of our retired shop floor workers did their back in at work (currently 20% of the shop floor is over 65, and two are over 80), I put a limit of 100 N.m on the torque tightening of nuts regardless of bolt size, just to prevent injury. We use a lot of nyloc nuts now!

The 2:1 reduction instantly suggests putting the leadscrew on the geartrain inside the belt box away from dust & grot. That would also mean the leadscrew handle can be left in place on the other end of the lathe for manual movements. I like that idea.

Regards,

Richard

[richardandtracyParticipant @richardandtracy]

John AS,

Thanks for your re-assuring words, and I shall follow your progress with interest.

Richard

[John Stevenson 1Participant @johnstevenson1]

Yes sorry typo, not got used to decimal money yet

Yes along these lines. best of both worlds and functional.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

**LINK**

(1) Read the articles by Dick Stephen .

He is/was an amateur engineer but very knowledgeable on technical matters generally and these articles are a rare example of something written by someone who actually knew what he was talking about .

(2) Leaving the ordinary handwheel in place is a bit of a mixed blessing when powerful stepper motors are involved . The values for holding torque – power on and power off – can be quite large and are also of a cogging nature so hand wheel can take a bit of effort to move and tend to go bump bump as it turns .

Works ok with little systems and gets to be more of a problem as things get bigger . An electronic handwheel is very easy to do and avoids these possible difficulties .

(3) You will need to think a lot about feed screws , nuts and end bearings . If you are retaining the as supplied items backlash will be a big problem . Some CNC software has backlash correction which can certainly help but when trying to do fine work on a basically clumsy machine it will prove inadequate .

Really ball screws and ball bearings need to be fitted . If this can't be done then upgrade the existing set up as far as possible .

(4) Don't make the mistake of assuming that a CNC machine is just a manual machine with steppers fitted – CNC is a whole new way of thinking and doing .

MikeW

Edited By MICHAEL WILLIAMS on 04/06/2013 09:37:07

[John Stevenson 1Participant @johnstevenson1]

Michael,

Very valid points but my reply was aimed at Richard who is interested in making some pens, not space shuttle parts.

If it had been for a different discipline then my reply would probably have been different

[richardandtracyParticipant @richardandtracy]

John is correct.

The Warco WMT 300/1 I have is a lovely little machine and I have learnt many of its ways. There is a lot of backlash: possibly 0.5mm at the headstock end of the leadscrew and 0.25mm at the other end. It means that I have to machine the same way every time, withdraw the cutter, move back etc. No great shakes, so long as you know AND DON'T FORGET (guess who has managed to wreck several threads when he did..   )  . I expect to use the same method of cutting on the cnc.

I really need a repeatability of 0.025mm and a theoretical precision of better than 0.05mm. I measure most of the diameters of my pens with a 0.02mm precision vernier caliper and try to machine everything so it's correct by that. You can feel a step when the diameter of two mating parts are wrong by 0.1mm even after polishing rounds the step. In fact, it's usually better to machine concentric parts togther in their final position, because slight errors in concentricity are really noticeable.

To give an idea: I machine most of the bits using an ER32 collet. The runout on the collet chuck I have is less than 0.01mm according to my dial gauge (the needle moves, but less than one segment, and it's not much worse than dialling the headstock on its own), however when one concentric part is machined one way and fitted into the end of another part machined the other way in the chuck, it's possible to feel two areas where there is perfect alignment and two areas where there is a step (one step on one part, the other step on the mating part). A pen is being used by the most sensitive part of your body, so exact dimensions are not hugely important but differences in sizes are.

However, that is not the biggest problem. Not by a long shot. The biggest problem by far is the flexibility of the plastics used. I have had, while doing rough turning (with 0.5mm deep cuts – any more & the plastic chips or melts with carbide cutters and doesn't cut at all if coolant is used), on a 105mm long barrel using a dead centre, the ends came out at 12.00mm diameter, and the centre was 13.96mm diameter. Purely due to work deflection over only 105mm. I have since realised that a steel mandrel down the pre-drilled core stiffens the barrel up by a factor of several hundred.

Now I want to use CNC to get exactly that sort of curvature, but in a controlled & repeatable manner. Silly really. Sigh.

Regards,

Richard.

edited to remove unexpected smiley

Edited By Richard Williams 7 on 04/06/2013 11:39:36

[Chris HeapyParticipant @chrisheapy71135]

For plastics you don't want to be using carbide, typically there is far less back rake and cutting pressures are higher thus pushing the work away from the cutting edge. HSS steel would be better, and grind exagerrated reliefs all around (think a knife blade whittling wood!). You cannot take big cuts with a tool like that as it will tend to dig in and pull the tool into the work (and vice-versa), but for shaving/finishing cuts on soft materials it will give you the most accurate result. Needless to say the cutting edge has to be razor sharp, and it will be fragile. If you recognise its limitations such a tool still can be useful. I use such a tool for cutting PTFE (carbon/bronze-filled PTFE) when forming seals and piston rings.

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