Author Topic: Small pantograph  (Read 16376 times)

Offline arnoldb

  • Administrator
  • Full Member
  • *****
  • Posts: 1338
  • Windhoek, Namibia
Small pantograph
« on: December 16, 2012, 06:40:20 PM »
I'll blame it on Zee and Jo  ;D - though I must admit that I have given building one some thought in the past.

I do have quite a few uses in mind for an engraving pantograph, and all of these requires it in reduction usage.  There are many pantograph plans available online - and I found one that would just about suit my needs - with a bit of modification.  The original is built of wood, but I prefer steel.  So I made a C-o-C of that one to fit my own needs, and added some simple refinements; primarily the use of bushes in the pivot joints rather than depending on bolts being accurate.  This is all to minimize backlash, so that I can get a hopefully rigid, yet easy and accurate to operate tool.

All the bits I need are fairly common, and even if the machine ends up as a dud or a not-used bit of tooling, nothing used in making it will go to waste.  There's always other uses for the parts I'm using to build it from.

OK, enough natter; I started off by sawing some calculated lengths of 25x5mm flat bar - they will go together in approximately this pattern:


Then I started drilling and reaming holes in the bits.  Quick and easy to do on the mill with the DRO - the holes do need to be spaced fairly accurately.  After all the small work on the Popcorn engine, it was really satisfying to just take a 16mm drill and poke a hole with it  ;D :


The parts after drilling and reaming holes.  All the 8mm holes were reamed to be nice and accurate in size:


Then I turned a bronze bush from some 3/4" bronze - with a 16mm lip to fit inside the 16mm hole I drilled in the one arm.  The bush has a 13mm ID that is _just_ larger than the knurls on the handle of my Dremel flexible shaft.  I then silver soldered the bush into the arm - making sure that the silver solder had penetrated all the way through the joint.  It's a small detail, but this joint helps to add back some rigidity that was lost by drilling that big hole in the arm:


After a quick brush-off to get rid of the flux, I just used a junior hacksaw to saw a slot on one side to approximately the center line of the bush, and then a quick cross-cut made for a section of the bush that can be used for clamping.  An odinary hose clamp provides the clamping power, and here the flexible shaft handle is shown securely clamped in the bush.  It's not pretty, but it is functional:


The project needs some large flat nylon washers - to fit between the arms to form bearing surfaces.  The larger that will fit, the better, as they will also add axial stability to the arms to keep all faces nice and flat.  I have about 4' of 30mm nylon (well, I think it's some kind of nylon - it's definitely one of the engineering plastics used to make bushes from), and I turned a section of that down to 25mm.  The swarf makes a really good kraaines (literally translates to "crow's nest" in English - we call an overrun on a fishing reel a kraaines in Afrikaans, and this looks like an overrun on a fishing reel):


Underneath all that swarf, the plastic actually ended up with a fairly nice surface finish:


After it was turned down to 25mm, I used the bed-mounted long range DTI to part off five 1.5mm thick washers.


For some reason they all turned out slightly dish shaped; my rear parting tool was not quite sharp enough - but the slight dish effect might have an advantage later on:


Four brass bushes followed - an accurate 7.98mm OD for a light slip fit in the 8mm reamed holes in the arms, all 11mm long, and drilled through 6mm for M6 bolt clearance:


I stopped there for the day.  I still need to make the rear mounting and pivot joint, and need to find a store that's still open this close to Christmas to get some M6 bolts / cap screws, nylock nuts and body washers.  The mill scale on the flat bar arms are quite rough around the pivot points - I'll check out how things feel once assembled, but I have a hunch I'll have to get rid of that crud before things will operate smoothly.  Anyway, here's where things were left off:

Hmmm... Note to self - there's only one battery left in that packet for the DigiVerns...  More to the shopping list.

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Online Dan Rowe

  • Full Member
  • ****
  • Posts: 747
  • Dripping Springs TX USA
Re: Small pantograph
« Reply #1 on: December 16, 2012, 06:51:04 PM »
Arnold,
Nice start and that photos of the swarf wound around the work reminded me of a similar job I did in plastic. It was doing the same thing and warping around the work. It was a small job on a Sherline lathe so I took it outside and flew the swarf in the wind like a kite on a string.

Dan
ShaylocoDan

Offline Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12769
  • Hampshire, england.
Re: Small pantograph
« Reply #2 on: December 16, 2012, 06:52:21 PM »
Looks like a good start...

Im assuming that the three holes have been drilled to give you some standard ratios, what sizes did you go for? I find that a really large reduction ratio is really useful if you want to follow a drawn pattern rather than just the copy, the odd little wobble with the hand doesn't show up too much that way ;).

It is also useful if you are making your own copy, which is  :Director: expensive stuff. Have you thought about copy mounting?

Jo
Enjoyment is more important than achievement.

Offline mklotz

  • Full Member
  • ****
  • Posts: 2406
  • LA, CA, USA
    • SOFTWARE FOR PEOPLE WHO BUILD THINGS!
Re: Small pantograph
« Reply #3 on: December 16, 2012, 07:13:51 PM »
When I used the Dremel flexshaft on my (similar) pantograph, I quickly discovered that it has a fair bit of axial endplay.  Setting the bur cutting depth with the Dremel powered down wasn't reliable.  The only way to get the depth I wanted was to make test cuts in a piece of scrap stock.

I'm not sure how or if this will influence your design but I thought I would throw it out for consideration.
---
Regards, Marv


Home Shop Freeware
http://www.myvirtualnetwork.com/mklotz

Offline zeeprogrammer

  • Full Member
  • *****
  • Posts: 6375
  • West Chester, PA, USA
Re: Small pantograph
« Reply #4 on: December 16, 2012, 07:20:09 PM »
I'll blame it on Zee and Jo  ;D

I'm in good company then.  ;D

Looking forward to seeing this in action Arnold.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13734
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Small pantograph
« Reply #5 on: December 16, 2012, 07:48:46 PM »
Great start Arnold. IIRC, the color of that nylon indicates that it is molybdenum disulfide (sp?) filled nylon....great stuff for bushings and washers aside from the birds nest that is :)

Bill

Offline Bearcar1

  • Full Member
  • ****
  • Posts: 704
  • Chicagoland Area, USA
Re: Small pantograph
« Reply #6 on: December 16, 2012, 09:31:21 PM »
What a cool and interesting project, Arnold. I'l be tagging along for the ride. I suspect the pins (pivots) will require a pretty close fit.


BC1
Jim

Offline Don1966

  • Full Member
  • *****
  • Posts: 6006
  • Morgan City, LA (Along the Gulf Coast)
Re: Small pantograph
« Reply #7 on: December 16, 2012, 10:03:33 PM »
I am interested in the results to Arnold, so I will be tagging along also. Oh!  and great start.

Don

Offline arnoldb

  • Administrator
  • Full Member
  • *****
  • Posts: 1338
  • Windhoek, Namibia
Re: Small pantograph
« Reply #8 on: December 17, 2012, 04:55:08 PM »
Thanks Dan - that gives me an idea; next time I'll switch the shop fan to full blast - it's hot enough here at the moment with regular 36oC+ temperatures.

Jo, Thanks.  Yes, I went for standard reduction sizes : 1/2, 1/3 and 1/4.  I haven't given copy mounting much thought; for now, I'll work off computer printed templates.  Like you say, the reduction can help hide wobbly operation.  I'll make up my own copy if I find I need it regularly.  For you it's just expensive; for me there's the added difficulty of getting it here.  I'll scour some of the local arts-supply shops though; I might just find something suitable.

Thank you Marv.  I've also noticed the axial play...  I'll see how things go, and if needed, I'll make up a small ER11 spindle that can be driven off the flex shaft.  That could be a very useful bit of kit anyway. 

Thanks Carl - Yes, good company  :ThumbsUp:

Bill, thank you.  Thanks for that info; I once had the "pleasure" of sticking a finger in a pot of pure molybdenum disulfide grease...  It was black for days afterwards  :facepalm2: - much worse than normal CV joint grease.  I do like this plastic though; it machines very easily and so far it does feel exceedingly slippery, so I'll live with the bird's nests  :)

Thanks Jim.  Yes, the fits in the pivots are crucial to accuracy; that's why I went for the bushes as inserts there.  Easy to turn up accurately, and not difficult to replace if they get worn.  The big washers are to add as much stability as possible to prevent the arms tilting with respect to one another.  And tightening up the bolts to _just_ the right settings will be fun too...

Don, Thanks.  I'll be sure to bore everyone with the results - be it good or bad.  Failure is an option here  :Lol:

Well, that's it for now; had a hectic Monday and didn't get to pop out for some needed bits.

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline arnoldb

  • Administrator
  • Full Member
  • *****
  • Posts: 1338
  • Windhoek, Namibia
Re: Small pantograph
« Reply #9 on: December 22, 2012, 06:50:12 PM »
Some more done - and the first less-than stellar results, though I was expecting that  :lolb:

I made some bits for the rear pivot joint from some odds 'n ends.  There was even some stick welding chicken-crapping involved.  Fortunately I have a small grinder  ;D :


Some more welding; this time slightly better...:


Then I assembled everything and bolted the rear mounting bracket to a bit of pressed wood left over from kitchen renovations a couple of years ago.  A bit of all-thread secured with retainer in the rear pivot will allow me to add spacers to lift things up as and when needed in future.  I also made a crude stylus from some more of the 6mm all-thread:


Eager to get the first test in to see what issues there are, I just clamped a block of wood to try and engrave.  No fancy engraving cutter either; a broken 1mm center drill has a 3.2mm (1/8") shank and chucks straight up in one of my Dremel collets.  The free-hand results to the right says it all  :lolb:


Everything is much too stiff still.  The flat bar bits as-is has a rough surface and adds a heck of a lot of friction; by the time the holding bolts are loosened enough to allow smooth operation, rigidity is out the window.  So all the pivot surfaces will be introduced to the flycutter to smooth them out.
The serious wobble on the down-stroke of the E in TEST was caused by the bit extending from the engraving carrier arm hitting my hand while manipulating the stylus.  That's not good.  For 1/4 reduction it won't be an issue, but for 1/2 reduction like I did this trial run, its a pain in the knuckle.  Literally.  The whole setup would work better if assembled the other way around for a right-handed person like myself.  For left-handed, it should be just fine.  I'm fairly ambidextrous, but usage of the pantograph is similar to hand-writing, and that's something I'm not even good at with my right hand :-[ .  OR...  I could leave things as-is, and instead of the "rear" pivot point to the back, just rotate the whole lot 90o counter clockwise...  I'll see about that.
I just used a 6" rule as a guide to "draw" the box around "test" - without any reference markings at all.  The boo-boo on the left line once again stems from things being too stiff - there's no "feel" to the stylus, and the whole setup followed it natural curvature - I didn't use force to keep the stylus against the rule.

The above sounds like a lot of doom and gloom, but actually I'm quite optimistic.  There's some things to sort out, some I expected and others not, but just a bit more work needed and things should be looking up  :) .

For now, I'm a Philistine.  Santa dropped in a bit early and delivered some good quality fermented and distilled grain produce originating from the far northern regions of the UK.  A good measure of that (several "glugs" worth) combined with purified and solidified  DiHydrogen Monoxide, and I'm a very content chappy  ;D - and to add to life's little pleasures, there's the soft pitter of raindrops on the roof - a welcome break after a ferociously hot and dry week.

 :cheers: , Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline IanR

  • Full Member
  • ****
  • Posts: 124
  • Derby, UK
Re: Small pantograph
« Reply #10 on: December 22, 2012, 07:12:22 PM »


 solidified  DiHydrogen Monoxide
Yup, philistine :Lol:

Offline Bearcar1

  • Full Member
  • ****
  • Posts: 704
  • Chicagoland Area, USA
Re: Small pantograph
« Reply #11 on: December 22, 2012, 08:02:15 PM »

Happy holidays Arnold, it appears that things have been moving forward. since your last post, I got to thinking, what if ball races were used as the pivots instead of bushings. That lead to a way of how to prevent what you are encountering. In my mind (yeah I know) it seemed that after getting the roller ball bearing(s) fitted to the arms, one could then utilize a very thin shim between the inner races to achieve the necessary clearance for the arms to not interfere with each other. Perhaps even a shoulder bolt arrangement for the pins such that a pre-load could be introduced, much like the front wheel bearings in automobiles. Of course these are the ramblings of one that is not actually performing the tasks at hand, so can be discarded as nonsense by those that are.  :slap:  Hopefully, over the holidays you will find some time to perfect your creation and we will all await with the H2O readily at hand  :cheers:


BC1
Jim

Offline NickG

  • Global Moderator
  • Full Member
  • *****
  • Posts: 1430
Re: Small pantograph
« Reply #12 on: December 23, 2012, 08:58:49 AM »
Nice 1 Arnold! Looks good to me  :ThumbsUp:

Offline Alan Haisley

  • Full Member
  • ****
  • Posts: 670
  • Near Clayton, North Carolina, USA
Re: Small pantograph
« Reply #13 on: December 23, 2012, 02:34:43 PM »
Arnold,
Would slightly longer arms help with this?
Alan
 
The serious wobble on the down-stroke of the E in TEST was caused by the bit extending from the engraving carrier arm hitting my hand while manipulating the stylus.
 :cheers: , Arnold
Near Raleigh, NC, USA

Offline arnoldb

  • Administrator
  • Full Member
  • *****
  • Posts: 1338
  • Windhoek, Namibia
Re: Small pantograph
« Reply #14 on: December 24, 2012, 07:05:18 AM »
Cheers Ian  ;)

Thanks Jim, and Happy Holidays to you and the rest as well  :cheers: .  I think your idea for using roller bearings is great; I wish I had a couple in stock!  They'll be able to take quite a bit of pre-tension as well; as things will not be done at great speed.  Hmmm...
Unfortunately an update will be a bit slow; I'm not having much in terms of time off for the shop - with a three day workweek this week and 24/7 standby duty...  At least I'll pop out to some friends for Christmas lunch and so on - so it's not all work.  If the new systems I'm working on are stable, I might just get to take leave for the 31st and turn next weekend into a long weekend  :)

Thanks Nic  :)

Hi Alan - yes, longer arms might help with it.  It's a bit of a balance between size and rigidity; the bigger one makes it, the heavier it must be built to maintain rigidity.  It's all very much experimental at this point anyway  :thinking:

Merry Christmas Everyone!

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!