Model Engine Maker
Supporting => Tooling & Machines => Topic started by: arnoldb on December 16, 2012, 06:40:20 PM
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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:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4749.JPG)
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 :
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4750.JPG)
The parts after drilling and reaming holes. All the 8mm holes were reamed to be nice and accurate in size:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4751.JPG)
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:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4752.JPG)
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:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4753.JPG)
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):
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4754.JPG)
Underneath all that swarf, the plastic actually ended up with a fairly nice surface finish:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4755.JPG)
After it was turned down to 25mm, I used the bed-mounted long range DTI to part off five 1.5mm thick washers.
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4756.JPG)
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:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4757.JPG)
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:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4758.JPG)
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:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4759.JPG)
Hmmm... Note to self - there's only one battery left in that packet for the DigiVerns... More to the shopping list.
Kind regards, Arnold
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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
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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
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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.
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I'll blame it on Zee and Jo ;D
I'm in good company then. ;D
Looking forward to seeing this in action Arnold.
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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
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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
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I am interested in the results to Arnold, so I will be tagging along also. Oh! and great start.
Don
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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
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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 :
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4760.JPG)
Some more welding; this time slightly better...:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4761.JPG)
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:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4762.JPG)
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:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4764.JPG)
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
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solidified DiHydrogen Monoxide
Yup, philistine :Lol:
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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
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Nice 1 Arnold! Looks good to me :ThumbsUp:
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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
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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
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Well, no leave for me on the 31st - I forgot I have to decommission the old systems at one customer ::) .
A bit done today - progress of sorts but still not satisfactory.
I took the fly-cutter to the mating surfaces of all the arms - skimming off 0.2mm to smooth things out around all the pivot points:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4766.JPG)
Then I assembled everything the other way around - to get the knuckle-knocking bit out of the way. I decided to plunge in with experiments on a bit of brass plate; I simply screwed my tooling plate to the pressed-wood base board The base board is not all that flat - I had to shim one end of the tooling plate up a bit to get things level. I made up a very crude engraving bit from an old 3mm drill shank; as the shank is soft I just turned a point on it and filed a bit of a flat on it. Far from ideal - but I decided to try it out anyway. A quick print-out from the PC provided the copy material.
The first test didn't go well at all. I found a lot of wobble between the flex shaft handle and it's mounting. What was happening was that it was not gripping properly on two sets of knurls to keep things stable - a paper shim in there cured that problem quick and easy. The spring washers I used were just too stiff; while the joints moved much more freely after flycutting the faces, the spring washers still added too much pressure, and by the time the bolts and nuts were loosened enough, things started to get wobbly; even with the close-fitting bushes in the joints, there is enough play to allow things to twist slightly. The 5mm flat bar is just too thin to make for reliable bushing in this application. I removed all the spring washers and just tightened up the lock nuts and then released each a tiny bit to just ease up the joints. This works much better, and everything works fairly smoothly.
The set-up after the trial and error work:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4767.JPG)
Even while improved, the results are still far from satisfactory though :embarassed: . Free-handing the job, even with the printed guide makes it look surprisingly like my own handwriting :lolb: . While doing the last bit, I did have a couple of major oopses while following the lines; I could feel them while going along. Gripping on that threaded rod stylus is definitely not comfortable. While engraving the surrounding box, I used a rule as a guide; that helped a bit, but for some reason the right hand edge has a wavy shape... I don't know if that's down to me, the cutter, or some free-play somewhere. Well, if it's the cutter or free play, it's still down to me :Lol: .:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_4771.JPG)
For now, I'll shelve this project - as much as I dislike doing that. I have a bunch of milling cutters on order, and I added a selection of proper engraving cutters to it. That will take about 4-6 weeks to get here. In the meantime, I'll scout some shops for goodies I can use as copy lettering - most local shops with anything that might be suitable will only open in a week or two anyway ::) .
Time for an engine build... I'll sleep on things and try to decide just what :thinking:
Kind regards, Arnold
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I was just thinking about this thread about an hour ago.
If I do finish Spinster and give it to daughter, it would need a plate.
Still thinking about a little x-y table with steppers.
Well you might shelve this project Arnold...but your projects need a nameplate.
Don't wait too long. ;D
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Commiserations :shrug:, it looks like your output is suffering from hand wobble due to lack of commercial copy ;).
Edit: Have you got any old drafting lettering stencils? 8)
Jo
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Arnold,
I think that black stuff you used for the washers is Vesconite.
http://www.vesconite.co.za/ It's good stuff but expensive.
All that 'wobble' seems to me that you have had too much wine over the Christmas period mate. :cartwheel: :lolb:
Guides for the stylus (pointed bit) is really needed, freehand is really difficult.
:cheers:
DaveH
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Look around for the templates that accompanied a Leroy lettering set, e.g....
http://www.mccoys-kecatalogs.com/KELeroy/3245-15L/3245-15L.htm
When I was young, (a long time ago; I lit the fuse on the Big Bang), we used these to letter titles on hand-drawn graphs and presentation slides.
They're still available on the bay...
http://www.ebay.com/itm/Leroy-Lettering-Set-Keuffel-Esser-CO-Vintage-Wooden-Box-Pens-NICE-/310401244987
but ask around the old-timers where you work. One of them might have one stashed in his desk next to his slide rule.
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Have you considered making washers from Teflon sheets to reduce friction?
How good is the engraving head bearing? I would think that having play in it could lead to the wobbly line.
Lee
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;) I won't wait too long Carl - things must just get back to "normal" here from the holidays... Just about everybody closes shop and go away; I'd guess at least 60% of residents leave town to go to the coast, South Africa, or the North of the country. It's amazing what it does for the morning "commute" to work though... My average travel time to my principal customer site goes down from about 20 minutes to 5 minutes :Lol: . If I don't get anything suitable to use as guides and satisfactory results, a CNC router / micro mill is still a viable option. I'll have fun building it, and I'm pretty sure I won't have problems operating it with available software; even if I have to study up a bit on G-code, it's just a programming language. Can't be much worse than C or the various assembly languages for different CPUs - though I might have to drop my Z80 or 8052 brain banks to add in the G-code one :Lol:
Thanks Jo. I've been digging through my old draughting stuff - I found all the old compasses, refillable ink pens, triangles and a couple of stencils, but the largest one I have has 6mm letters and is designed for 0.5mm ink pens. It might be usable with a suitable tip on the stylus, but it's NBG for making copy from... In the meantime, I'll see what I can scare up from art/stationary suppliers for bigger stencils :ThumbsUp:
Cheers Dave :cheers: - It's not quite Vesconite; it's lighter in colour. The local branch of Huster Machine tools have a nice rack full of Vesconite standing right in their showroom. My wallet cringes every time I walk past that rack - I once bought some of it to make a shaft bush for a high-speed printer from. Fortunately they sell it by the cm :-X . The wobble might be withdrawal symptoms; I've had a pretty dry holiday season so far :lolb:
Thanks Marv - that's some seriously nifty kit! I've never seen something like it; I wish I had it in school for my draughting classes. Alas, somehow I'm turning into the "old" guy in the circles I move in; I'd take the kit and slide rule off anyone that has it, but the crowd I mostly come into contact with can't do anything without computers and Google. Or bl**dy "smart phones"... I'd better stop before I go into a rant.
Lee, thanks. I was hoping the washers would do the job as-is. Teflon sheeting's a bit scarce around here, but I'll keep my eyes peeled for some. Or I'll go with roller bearings; that should sort things out nicely as well. I'm not too sure about the flex shaft's bearings; I cant detect any lateral play on it, but it could be a factor. I'll see what happens once I get the proper engraving bits though - the crude one I made is far from ideal.
Kind regards, Arnold
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Teflon sheeting's a bit scarce around here, but I'll keep my eyes peeled for some.
Teflon sheeting is sold as non stick baking sheets for use in the kitchen ;).
Jo
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Nice tip Jo, I'll file that in the top drawer. Arnold the stuff you used loks like delrin to me. I use it for bearings and so forth and while it gets rat nests I found it helps to throw a trand over the splashback of the lathe into a bin and it just goes nice. Nice to work and real good finish. Seeing this build I am thinking of a similar setup using the dremel. I have a larger set up which uses my router for making nnameboards an signs.
Pete
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:) Thanks Jo - I'll add kitchenware suppliers to my list of shops-to-visit. Those sheets could even come in handy the next time I bake biscuits.
Pete, thanks. It might very well be Delrin - I'll try it out for bushings at some point and see how it works. I know the white PTFE I have is great for bushes as well; the engine I built using it runs slick as anything. This feels slightly harder than that PTFE; it might ream better; I had a bummer of a time reaming the PTFE to size. I'll play around when the occasion arises.
Kind regards, Arnold