Virtual shop tours

#1
One of the things that has come up during a few of my conversations both at the symposium, and via email since, is that plenty of people have never seen a straight line engine in the flesh, or in use. Is there any interest in using video online to do virtual shop tours? I'd be happy to chat via Skype one on one, or use Google Hangouts for several people at once. This is probably most useful for people who have engines and don't know much about using them, but it could be helpful for others as well.

Let me know here in the forum if there is any interest in doing group chats about engine turning, and if you're interested in something one on one, send me an email.
 
#2
Chris
This is a bit of a seqway from your idea of a virtual shop tour but at one point in organizing the Symposium David was considering having a session on straight line math. I would certainly have attended that but it's not the sort of topic that would interest a lot of people. That said, how much difference is there between rose engine and SL math? My sense is that for anyone who is just starting out with a SL machine (and for those like myself who are still grappling with one), the math involved is a bit of puzzle and it's not helped by some weird pitches used on the lead screws of different SL machines. For example, a simple question we all face, how far should one advance the ratchet cross slide in order for the next cut to just touch the previous one? This will depend on a number of factors but there must be some basic geometry that those who are more skilled in this than I am (almost everyone!) can explain to the forum. Another one; in rose engine work I think the radius of the geed should be half the radius of the sine wave rosette in order to cut a proper sine wave. Is this the same for SL?

Many of these math questions don't come up until one actually starts doing SL work; until then they seem pretty boring and academic. But without a decent reference doc on the mathematical relationships a lot of SL work is trial and error - even for simple SL machines - at least it is for me. Has anyone found such a document that can be applied to SL machines generally?
Ramsay
 
#3
Ramsay,

This is exactly the kind of thing that is challenging to write about and ask about, and often much easier to explain over a pint, or via video chat (when visiting David in August, he explained a pattern to me in 5 mins that would have taken days to sort out by email). The simple answer is that yes there is a bunch of important math, the math is mostly the same between RE and SL work, and yes we need to document it. I'm happy to chat either here on the forum, or via video about this stuff. As we do, I'll start documenting it in a way that makes sense.

As for your specific question about sine wave bars, it's the rubber, not the guide you should be concerned about. The guide is just to prevent the cutter from going in too deep. The rubber should be half the radius of the smallest radius on the rosette/pattern bar to achieve the ideal pattern. You may change it later on for other effects, like softening a pattern, but the ideal is often what we want. I encourage you to experiment with other rubbers, but always keep an ideal one on hand for each pattern.

My idea for doing a google hangout came from a photographer I follow. He usually has 6 or 7 people together in the chat, and he does a Q&A session up front. He then follows it up by doing a demonstration at the end. The first bit is nice because you can hear other people's questions, and they may lead to either your own questions, or an understanding of something you didn't know was important. The second part is nice because you get to see someone who knows what they are doing actually demonstrate technique. He records all of the sessions and posts them online for others to see later on. If we kept it to let's say a one hour session once a month, that might be feasible for people to join in and learn something.

Let me know what you think.
 
#4
...The rubber should be half the radius of the smallest radius on the rosette/pattern bar to achieve the ideal pattern.
Can someone enlighten me on where this comes from? Two of you guys have said this now assuming that Ramsay really meant rubber instead of "geed." What does "ideal" mean? If it means "identical" to the rosette or pattern bar then the math doesn't support that. E.g. a sine wave on a pattern bar will be duplicated as a sine wave with a sharp rubber ( zero radius ). Much the same with a rosette except for the apparent distortion you get depending on the radius of your cut. Inner curves start turning more into cusps as radius decreases.

I'll try to demonstrate my point with some boring equations and graphs shortly but it'll take some time to draw them up. Basically the bigger radius you have for a rubber, the bigger distortion you get from the original pattern and it's directly proportional to the cosine of the tangent angle (point of contact or slope of the pattern) between the rubber and the pattern.

If "ideal" means pleasing to the eye then anything goes ... ( colon right parenthesis - smiley face thing )

(can't find a way to add an emoticon and I'm in the "advanced" reply mode...Even if I type in "colon right paren" it disappears)

Cheers,
Rich
 
#5
Traditional sine wave bars are not actually a sine wave themselves (the peaks are cut differently than what they'll appear on the pattern). It relies on having the correct rubber to generate the sine wave. The issue is that you can't have a zero radius rubber, and a rubber with a radius that is too small can have issues traversing certain parts of the bar (not to mention be difficult to maintain). For example, the basket weave bar that we both own. A knife edged rubber doesn't work as well as one with a 0.006" tip on it. The knife edge has difficulty getting out of the valleys, and skips over the peaks too easily.

I have a sine wave bar that's been cut as a real sine wave. I have to use a knife edge rubber on it to get something resembling a sine wave on the final piece. The result is poor compared with my sine wave bar that requires the use of a larger radius rubber to achieve the sine wave pattern (they are nearly identical in terms of amplitude and period).

As for ideal shape, it depends on what you're trying to do. Most of the time when I use a sine wave bar I want a sine wave pattern on my piece. So I use the rubber that gets me that shape. But sometimes I want scallops from that bar, so I use a different rubber. Daniels has a description on how to shape rubbers for effect.
 
#6
Thanks, still don't know where the "half radius" comes from and what kind of bar or rosette it would apply to. It also sounds like you're trying to distort a non-sine wave pattern into a sine wave pattern with a larger radius rubber. That sort of works when the pattern bar or rosette is a zig-zag as the larger rubber can smooth some of that out. That also works with a negative scallop bar because the larger rubber rounds out the sharper peaks. So you can contrive something like a sine wave out of a negative scallop bar but the inverse, or any other regular pattern won't do it. Attached picture shows what I mean by a negative scallop.

I'm puzzled as to why, with a sharp rubber, you have trouble getting a nice sine wave out of a real sine wave bar. Also, I use a sharp rubber on the basketweave bar (and others) and don't have trouble with sticking and skipping. That bar was designed to keep angles below that which would cause sticking. A humble suggestion is to make sure there's not too much spring pressure on the pattern bar.

Could you post a picture of what you're calling a traditional "sine wave bar" that is not a sine wave? I'd like to add that to my education.

Still working on equations...

Thanks and cheers,
Rich
 

Attachments

#7
Here are three pattern bars. The first two will produce a sine wave, the third will not (the first two were cut so that a rubber with a radius of half of the valley will cut a true sine wave). The last one can get close, but it is obvious in the final piece that it's not a sine wave. I have yet to find any spring tension that will allow me to use a knife edge rubber effectively on either this third bar, or the basket weave bar. With the basket weave, I can achieve significantly better results with a 0.006" rubber than I can with a knife edge at any spring tension. I'm not sure about your rose engines, but my Field has scalloped rosettes for use as sine wave patterns.

I know the Daniels reference for the 1/2 radius, and I believe Matthews also references it. Perhaps David or someone else can step in and tell us about other references to it (i.e. Holtzapffle or Evans).
 

Attachments

#8
Yep, I see it - I have a hard copy of that piece of Daniels that I had forgotten about. Thanks for the reminder. It's clear to me that he sets out with the 1/2 radius as a starting point on that negative scallop rosette to see how the pattern looks and even says later that adjustments may need to be made (bigger, smaller rubber) depending on workpiece diameter to get the "ideal" barleycorn wave.

Mystifying - your problem with a sharp rubber on a smooth sine wave bar...

The spring pressure on my bars is 22lbs

Now that I think it's clear that this rubber question is about turning negative scallops into more regular waves I won't bother with the math exercise. Whew!

Cheers,
Rich
 
#9
I don't think it's mystifying. A sharp edge will never be as effective a bearing surface as a rounded one. That's why the original rosettes and bars were made with the assumption of a rounded rubber.
 
#10
Chris and Rich,
I was stuck in Toronto traffic for a good part of the afternoon so it was fun to read what you folks had been up to when I finally got back to the computer.

Yes, I meant rubber, not geed. Sorry 'bout that!

I've been under the impression that to replicate a sine wave rosette or pattern bar with a fine point rubber it would be essential to always have the "fine point" aligned directly with the center of the rosette or, in the case of a pattern bar, with the imaginary center which would have been used to create the pattern bar radius. If the fine point weren't aligned directly then the side of the rubber above or below the point would touch the rosette or pattern bar and would therefore fail to create an exact copy of the bar's or rosette's radius. (The problem wouldn't end there; even if the point could be kept aligned, the slide would have to move back and forth by the same amount that it would if the rubber were horizontal and aligned with the center.) Whether that's true or not, that's been my understanding.

The reason I think Daniels and some others have recommended that the rubber be half the radius of the pattern bar/rosette is because they recognized that it would be next to impossible to get a functioning mechanism to keep the fine point aligned as described above. So, if the fine point is one extreme and a rubber which is the same radius of the pattern bar is the other, then 1/2 the bar or rosette's radius (an average radius if you will) would be the most workable arrangement to copy the sine wave in the pattern bar or rosette. In short, I saw this as a practical and effective response to the mathematical challenge.

Chris, I'd never heard of a google hangout so I googled it. I guess the first challenge would be to get enough people on line at the same time for this to work. Not a deal stopper but would take a little coordination. I can work my schedule around whatever you'd like to put together so let's give it a try. I have a Kenloc so the numbers would be different than with your Plant but I'd really like to see you or Rich go through the mathematical and machining steps to create a simple sine wave with one of your machines. Let me know if I can assist in any way. We might get some participants who have LRW and straight line chucks but my impression (only that) is that not many of them are using them in the SL mode. Maybe this would help them buy into their machines' SL capability although they'd be using rosettes not pattern bars of course.
Regards
Ramsay
 
#11
I need to figure out what camera to use and setup so I can show the work effectively. Ramsay, perhaps once I've got that figured out we can test a hangout and make sure it works effectively. I think if we schedule a hangout once a month on a Saturday or Sunday afternoon, we should be able to accommodate most people's schedules. We can also make the video available later on for anyone interested. To start with I'd only be able to demonstrate straight line work, but in the new year I will be able to show off some rose engine work. And of course this is only for engine turning. I'm not the person to chat with about OT work…
 
#12
Chris and Rich,
I was stuck in Toronto traffic for a good part of the afternoon so it was fun to read what you folks had been up to when I finally got back to the computer.

Yes, I meant rubber, not geed. Sorry 'bout that!

I've been under the impression that to replicate a sine wave rosette or pattern bar with a fine point rubber it would be essential to always have the "fine point" aligned directly with the center of the rosette or, in the case of a pattern bar, with the imaginary center which would have been used to create the pattern bar radius. If the fine point weren't aligned directly then the side of the rubber above or below the point would touch the rosette or pattern bar and would therefore fail to create an exact copy of the bar's or rosette's radius. (The problem wouldn't end there; even if the point could be kept aligned, the slide would have to move back and forth by the same amount that it would if the rubber were horizontal and aligned with the center.) Whether that's true or not, that's been my understanding.

The reason I think Daniels and some others have recommended that the rubber be half the radius of the pattern bar/rosette is because they recognized that it would be next to impossible to get a functioning mechanism to keep the fine point aligned as described above. So, if the fine point is one extreme and a rubber which is the same radius of the pattern bar is the other, then 1/2 the bar or rosette's radius (an average radius if you will) would be the most workable arrangement to copy the sine wave in the pattern bar or rosette. In short, I saw this as a practical and effective response to the mathematical challenge.

...
Regards
Ramsay
We're mixing rose engines, straight line engines, and combos and getting muddy. You wouldn't want a sharp rubber on a rose engine primarily because it would dig into the soft materials that the rosettes are made from. You can and do use sharp rubbers on the hardened steel pattern bars of straight line engines. There's no bearing area worry on hardened steel with these machines but there is on soft rosettes.

I think the 1/2 radius starting point that Daniels describes is a very clever way of initially approximating the desired shape of a wave pattern on a rose engine workpiece and that technique can be used to get a wavy line starting point from a zig-zag pattern bar if that's all you have. I mean, the whole idea of varying rubber shape is to vary, in a pleasant way, the pattern that's cast in steel, or bronze. (stating the obvious in this forum)

Welcome back from traffic!

Cheers,
Rich
 
#13
It appears that you all have it worked out before I even saw the thread. This sine wave issue is very important for patterns such as chains and "basket weaves" (a term used for more than one pattern it seams). I have a short treatise mostly written on the subject that I really want to finish but the work schedule has been an impediment. I know that Rich L will add equations to it that will appeal to the better mathmeticians, to be sure.

To address Ramsay's comments about the funky lead screw pitches, etc. the Kenloc with it's 12 TPI is really not as bad as it would at first appear to be; however, the solution that we came to with Eric Spatt's Gudel for which he had no matched pattern bars was to use an electronic dial indicator. This reduced his mistakes to almost nothing. Further down this line of thinking the biggest difference between the rose engine math and the that of the straight line is that phasing on the rose engine is usually set out in degrees, especially when using the worm, where on the straight line the pattern bar tower movement is put forth in terms of distance; however, each one of them applies the same principles of phasing in that a percentage of the period is being divided. Also, the patterns translate directly between the two mathmatically and can be stated in terms of an equation.

Ramsay, I do believe that the microscope of the type you just borrowed will be a big help. I'm hoping to get some time soon to put one to use and make some videos. If a picture's worth a thousand words a video would be invaluable.

David
 
#14
I have been making YouTube videos for yrs. I've tried to shoot things in my shop I thought folks would like to see. The videos have been seen over 100,000 times. I have done Face Time for a guy who had a lot of questions about old machines. This was the way to go as he had a lot of questions.
 
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