Contact area for rubber next to cutter

#1
After watching the RGM and Vastin Constantin guilloche videos on youtube, and Rich's video on cutting the pen tube on his straight line machine, it appears that the contact surface of the rubbers of those machines is rather long. In the setup that I got from David, the rubber only provides a point on contact, which leaves a rather well defined line. I made a rubber from African blackwood that has a longer and a wider bearing surface, but it scuffed the surface of the piece instead of leaving a "black line" that is mentioned in Daniels book, and has been mentioned in some posts here.

Are my observations correct that the bearing surfaces of the rubbers of those machines are longer and not just a mere point? If so, about how long and how wide? I have some white nylon material that I can make another rubber from.

Thanks for your help.

Danny
 
#2
Hello Danny,
When you refer to "rubber" in your question I assume you're thinking of the guide which sits right beside the cutter in the tool holder. If this is the case, in Figure 28 of his now out-of-print book on Engine Turning-1680-1980 Martin Matthews showed sketches of two different types of guides. The "London" type has a large number of nose end shapes whereas the nose on the "Birmingham" guide is rounded and polished, more akin to David's guide than the London type. According to Matthews the advantage of the London guide is not only its greater height adjustment capacity but, particularly for SL work, the much wider wide nose allows the tool "to be guided onto the bottom and off the top of a workpiece without the tool digging in. I posted a picture (under the user name Tzam) of some Plant SL London guides in the Gallery back in 2010; it's not as helpful as Matthews' sketches but will give you a sense of things.

I have made a number of guides for rose engine work from acetal (essentially the same as Derlin) since I found the blunt but pointed steel guide that came with my machine was too wide to let me get close to the "wall" of an inlaid pattern. The acetal guides don't last very long but you can trim the nose to be quite narrow, allowing them and the cutter to get very close to another, previously cut pattern. I have made them with a rectangular nose approximately 1mm wide and about 3mm high. In that shape they do quite a good job acting as a guide on small (1" diameter) fine silver discs and the natural lubricity means they don't mar this soft metal. However, the acetal is easily damaged when, invariably in this type of work, they are run over previously cut engine turned patterns or "walls". Consequently, they need to be touched up fairly often.
Ramsay



After watching the RGM and Vastin Constantin guilloche videos on youtube, and Rich's video on cutting the pen tube on his straight line machine, it appears that the contact surface of the rubbers of those machines is rather long. In the setup that I got from David, the rubber only provides a point on contact, which leaves a rather well defined line. I made a rubber from African blackwood that has a longer and a wider bearing surface, but it scuffed the surface of the piece instead of leaving a "black line" that is mentioned in Daniels book, and has been mentioned in some posts here.

Are my observations correct that the bearing surfaces of the rubbers of those machines are longer and not just a mere point? If so, about how long and how wide? I have some white nylon material that I can make another rubber from.

Thanks for your help.

Danny
 
#3
Thanks for the reply Ramsay. I looked at your photos and Rich had a couple as well. They were helpful. I also looked as some drawings in Daniel's watch making book which is also out of print. The material that I said was nylon is more likely white delrin. I'll try making a guide from it and let you know how it works out. I'm also going to make a new cutter so that I can get closer to the edge of the discs that I'm holding in a bezel chuck. I'm cutting 1 1/8" to 2" Argentium silver discs. Do you know if Argentium silver is softer than sterlling silver?

Another question: I noticed in Daniel's book that he suggested a positive rake on the top of the cutter. Any thoughts on what kind of rake works best on the top side of the cutter. The one I'm using has no rake and seems to want to dig in the silver. When I cut test patterns in Nickel silver, which is considerably harder, the cutter doesn't seem to want to dig.
Thanks again,
Danny
 
#4
Argentium Silver is more tarnish and firescale resistant than regular sterling. It also has a smaller grain size than standard sterling and this helps in certain fabricating. Whether it's harder or softer than standard sterling seems to be a much debated question. From data in Mark Grimwade's "Introduction to Precious Metals" Grimwade lists standard sterling in the aged state is 120-140 HV, Argentium is 100-120 HV. Cold worked standard sterling hardens to 140-180 HV and Argentium hardens to 150-160 HV. There was a fairly long thread on this on the Ganoksin forum in 2010 and the experts seemed to be of the view that the differences in hardness alone aren't great enough to be a significant factor in choosing one alloy over another. There are other significant differences between the two that usually cause one person to prefer one alloy over another. For example, the germanium in argentium makes enameling pretty much impossible so I have not engine-turned argentium. Accordingly, I can't tell you from my own experience whether it is easier to engine turn argentium than fine silver, Sterlium Plus or standard sterling. I have only used the last three of these.

As for a new cutter to get closer to the edge than the 1/4" Micro 100 metal lathe cutters I had the same issue and started by using a Taig parting tool, mounted upside down and ground to the Daniels' specs. This worked pretty well but Rich encouraged me to look at using carbide which I subsequently did and have since retired my Taig tool. The cutters I use now are from Travers Tool and are Left Hand style Micro-100 cut-off tools with a 1/4" shank. The Travers part number is 21-100-907 and the cutter width is 0.040".

I won't say that it totally stops my digging into the work but I have always put a very slight negative rake on the top of the cutter. It's just a very tiny chamfer on the cutting edge and is difficult to see except under a bright light where it appears as a white line. Again, this was recommended by Matthews and I find that it certainly reduces but doesn't eliminate the dig-in possibilities.
Ramsay

Thanks for the reply Ramsay. I looked at your photos and Rich had a couple as well. They were helpful. I also looked as some drawings in Daniel's watch making book which is also out of print. The material that I said was nylon is more likely white delrin. I'll try making a guide from it and let you know how it works out. I'm also going to make a new cutter so that I can get closer to the edge of the discs that I'm holding in a bezel chuck. I'm cutting 1 1/8" to 2" Argentium silver discs. Do you know if Argentium silver is softer than sterlling silver?

Another question: I noticed in Daniel's book that he suggested a positive rake on the top of the cutter. Any thoughts on what kind of rake works best on the top side of the cutter. The one I'm using has no rake and seems to want to dig in the silver. When I cut test patterns in Nickel silver, which is considerably harder, the cutter doesn't seem to want to dig.
Thanks again,
Danny
 
#5
Ramsay, you're a wealth of information. I really appreciate all of your input. The cutter style you mentioned is exactly what I am looking for. The next time I order, I'll get one. I'll try the rake as well. As I try new patterns and work on different sizes of material, I'm learning quickly that there are things that need to be done to improve the quality of my work.
You've been a tremendous help. Thank you very much!! Hope you and your family have a great Thanksgiving.

Danny
 
#6
You're most welcome Danny. Enjoy your Thanksgiving!
Ramsay



Ramsay, you're a wealth of information. I really appreciate all of your input. The cutter style you mentioned is exactly what I am looking for. The next time I order, I'll get one. I'll try the rake as well. As I try new patterns and work on different sizes of material, I'm learning quickly that there are things that need to be done to improve the quality of my work.
You've been a tremendous help. Thank you very much!! Hope you and your family have a great Thanksgiving.

Danny
 
#7
On Argentium vs Sterling vs fine silver.

Argentium and Sterling are very very similar in how they react to engraving. Argentium can be heat hardened, while Sterling can't. This won't be a concern for most people. The low tarnish is the most desirable feature. Fine silver is softer, and more gummy when engraving. I find I need to take very light cuts initially to prevent tear out.

I mostly use Argentium in my work, and fine silver when I'm enamelling. It's rare that I find the need to use Sterling.
 
#8
Thanks Chris. I've been getting my Argentium discs from Rio Grande, but it looks like they are downsizing their inventory of larger discs. Do you guys have another source for Argentium stampings? Am I going to have to buy it by the sheet and get discs stamped?

Danny
 
#10
Danny
In view of the difficulty in getting a suitable range of argentium stampings you might want to consider Stuller's Sterlium Plus alloy. It's similar to standard sterling in that it still is 92.5% silver but it contains zinc and proprietary metals in place of some of the copper and is available in a wide range of shapes and gauges. Stuller claims it is tarnish resistant for two years and is harder than sterling. See Stuller's summary at: http://www.stuller.com/pages/3322

They have lot's of other sizes but by way of illustration their 2" round Sterlium Plus 20 gauge stampings are shown at: http://www.stuller.com/products/3100/3621174/?groupId=17406
Although I haven't used argentium I've engine turned Sterlium Plus and I found it easier to work than fine silver and about the same as standard sterling. It's a bit more expensive than the latter but is certainly more tarnish resistant.
Ramsay
 
#11
Hey Ramsay. I looked at the Sterlium plus listings on Stuller's website when you mentioned them earlier. For every size that I use and some more this note was the at the bottom of the page...
"We do not normally stock this item.
Out of Stock and Special Order items will ship when available."
It also looks like its rather difficult to open an account at Stuller's.
I'm going to call Rio Grande next week and see what the deal is.
Thanks for your help.
Danny
 
#12
Hi Danny
Yes, I'm aware of the note on Stuller's site. They have that on a lot of their product listings and also something about items being heavy and shipping might be expensive but when it comes to ordering I've found that they usually have what I want and the shipping is quite acceptable considering the weight. Stuller has a good reputation and is a big supplier to the jewelry trade. They sell a lot of finished jewelry, in addition to tooling and metals, and are trying to steer away from retail customers who might only buy one or two items and/or are price shopping against their local jewelry store which might be a volume purchaser from Stuller. That said, they are in a tough, competitive business and certainly want more customers. I'm not a volume buyer but had no trouble setting up an account with them a couple of years ago. If you're unhappy with what you find with what you learn from Rio you might give Stuller a call and see where it leads.
Ramsay

Hey Ramsay. I looked at the Sterlium plus listings on Stuller's website when you mentioned them earlier. For every size that I use and some more this note was the at the bottom of the page...
"We do not normally stock this item.
Out of Stock and Special Order items will ship when available."
It also looks like its rather difficult to open an account at Stuller's.
I'm going to call Rio Grande next week and see what the deal is.
Thanks for your help.
Danny
 
#13
After watching the RGM and Vastin Constantin guilloche videos on youtube, and Rich's video on cutting the pen tube on his straight line machine, it appears that the contact surface of the rubbers of those machines is rather long. In the setup that I got from David, the rubber only provides a point on contact, which leaves a rather well defined line. I made a rubber from African blackwood that has a longer and a wider bearing surface, but it scuffed the surface of the piece instead of leaving a "black line" that is mentioned in Daniels book, and has been mentioned in some posts here.

Are my observations correct that the bearing surfaces of the rubbers of those machines are longer and not just a mere point? If so, about how long and how wide? I have some white nylon material that I can make another rubber from.

Thanks for your help.

Danny
Sorry this post is so late as I just got my registration sorted out so I can post again.

The actual contact surface of the guide in my straight line and rose engine turning is really a point contact. The guide "possible" contact surface is curved in case I get into curved or angled surfaces to engrave. There are several pictures of magnified guides and the light marks made by them on the silver surfaces I do. The marks made by the guide are easily polished out without rounding out any of the bright-cut engraving.

For a special job I did, I shortened (vertically) the length of the guide so as to get close to a boundary cut but since the contact point is indeed that, there was no problem. The thumb pressure is roughly half a pound (really guessing) but it is not excessive as to leave a score in the material. There is also no rake (zero) in the cutters I use. Digging into the material should be limited by the guide and the setting I use for most of my work is 80µm (~.003") depth of cut (DOC).

I think a plastic guide is a wonderful idea and I think I might use Delrin AF as the material because it has teflon in it. I would not use a more "compressive" plastic such as ABS or polypro or nylon for that. By the way, the guides I use now are polished HSS.

My experiences and 2¢.

Cheers,
Rich
 
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