The Sherline Miniature Machinist's Newsletter
Customer Project of the Month
Extremely tiny watch parts can be made on Sherline tools, but sometimes special techniques are required. Magnification of the tool and work using a mill-mounted microscope (P/N 2127) is almost a requirement when working on parts this small and intricate. Jerry Kieffer is an expert at making very small parts, and he explains here how he went about it. Though you may never have to make parts this small, you will probably find it interesting to see how it is done.
A replacement watch escape wheel with center pinion is seen resting between pennies for size scale. A specially ground stone is used for one of the final operations. See below for the sequence of producing these shapes.
ìOver the years and again recently I have occasionally been asked how I cut watch escape wheels. Rather than give a long explanation each time, I thought I would explain a recent example here to refer to in the future. Hopefully it will also be of some interest to others.
I was recently asked to repair a Swiss "Huguenin" 18L pocket watch. To make a long story short, it had two busted escape teeth due to a poor repair procedure in the past. Surprisingly, there was no other damage. Even though it was a higher grade movement, it would not normally warrant this type repair effort. However, in this case it had a military inscription to a known individual and required repair with cost being of little concern.
When planning a job such as this, I take great effort to place myself at an advantage regarding cutting tool visibility, accuracy and efficiency.
The first concern when cutting a wheel such as this is the arbor and wheel blank. Because of the size (.270" or 6.85mm dia.), I do not use an arbor or wheel blank. Instead, I machine the wheel on the end of solid stock that also allows me to part off extra wheels. I find I can machine small wheels more accurately with this setup because it is far more rigid. In this example the teeth were machined .100" long allowing three wheels to be parted off in the lathe when machining was completed.
For horological wheel and pinion cutting, I no longer use anything other than an appropriate size milling machine. Their simple setup, accuracy and efficiency are unequaled for this type work.
For indexing, a rotary table was selected over direct indexing because of its many advantages. The rotary table allows for highly controlled and accurate positioning of a wheel tooth in relation to a cutter. Once in position, indexing can begin at that point. In addition, slight corrections in position can be made at any time and indexing can resume at that exact position. For this setup the rotary table was center positioned at the rear of the mill bed facing forward. This allows the wheel blank face to also face forward directly behind the cutter. This in turn allows for maximum cutter visibility by eye or microscope. The general arrangement can be seen in the first attached Photo. (Sorry about the photo quality but will give the general idea.)
For monitoring the cutting process, a spindle head-mounted microscope is used. By mounting on the spindle head, the scope remains in sharp focus while tracking the cutter tip. If not head-mounted it is very difficult to keep the scope in sharp focus with a moving cutting tool, especially at higher powers where focus is far more sensitive. In addition, the scope can be rotated to the side for easy tool access while remaining in focus.
Photo óMill set up with microscope and stock mounted in rotary table. The raw brass stock was threaded 3/8-16 on the end to thread directly into the center hole of the rotary table.
When setup as in the first photo, the first cut on the face of the blank is made with the side of an end mill. By rotating the blank against the side of the rotating end mill, a small centered stub is machined on the end of the blank. This stub is sized to fit the center hole of the original escape wheel. The wheel is then placed over the stub. This allows the cutters to be very accurately positioned using the old wheel as reference under microscope observation. No measurements are required when using this procedure. Cutter position accuracy is really amazing at 30x and higher. Cutter tip axis control and R/T rotation control make alignment simple, easy and highly accurate.
Photo 2óCutter for first cut.
The position of the cutter for the first cut can be seen in the second photo. The wheel shown is one of the extra wheels that was parted off. It is shown on the outer edge of a US quarter for size comparison. The cutter is, of course, not in the exact location for a cut but shows the general location for the cut. This cut removes more metal than the others so it is made first. This simple cutter was machined as a single point cutter and hardened for use. It was the only special cutter required for cutting this wheel. Cutter speed was about 500 RPM. The rest of the cuts were done with a standard .022" solid carbide end mill. Carbide was selected so that cutting fluid would not be required, allowing chips to be cleared with a constant flow of air. This allowed clear vision of the cutting process at all times. Cutter speed was about 2500 RPM.
Photo 3óEnd mill angle for 2nd cut.
The third photo shows the end mill location for the second cut. It was done while maximum strength was still left in that area.
Photo 4ó Third cut.
The fourth photo shows the third cut positioning. Once completed, an additional smaller cut was made to remove the remaining metal in that area.
The rotary Table was rotated slightly before this cut was made to get a slight radius to match the original wheel.
Photo 5óFinal cut.
The fifth photo shows the position of the final cut using the side of the end mill.
Photos 6 and 7óSpecially ground stones to finish the transition areas between cuts.
When the wheel was parted, a single light swipe with a very fine miniature stone blended the cut overlap and completed the contour.
At this point the rotary table is placed flat on the mill bed with the face of the cut wheel pointing straight up. This allows the crossing of the wheel to be done with a small end mill while rotating the R/T and moving the slides as require under microscope observation. Sharp corners are touched up with a small needle file if required.
Once parted, the wheels are then placed in a machined exact fit WW pot collet where the center hole is drilled/bored. Boring the collet and then the center hole assures centered arbor mounting. The sample shown, of course, was not used and was never center bored.
From start to finish this job took about three to four hours as I recall. That does not include phone calls, walking the dog etc. In this case the wheel functioned perfectly without any modification other than final polishing.î
This and thirty-six more projects can be seen on the Sherline web site at www.sherline.com/workshop.htm. Photos can be enlarged there for greater detail.
Shop Tip of the Month
I found a cruder/much larger version of this alignment tool online, but modified it for miniature lathe users. I do cue stick repair and restoration, so this is extremely useful in my business. I thought it may useful for someone with similar needs. The shank is 3/8" square T6 aluminum and the bearing is from a skateboard.
This procedure is designed to bridge the gap between the somewhat slow, but highly accurate independent 4-jaw chuck and the more convenient, but less accurate self-centering 3-jaw. With practice and patience you will become faster and get better results from the self-centering units. I use my tool for aligning joint pins on damaged custom cue sticks, but regardless of your interests, anything to increase accuracy and save time is worth trying.
The holder uses a simple 3/8" shank held† in the P/N 7600 tool post. A skateboard bearing is attached to one end. (Click on any photo to view a larger image.)
Using the Centering Device
To align a reasonably round object, slightly loosen the 3- or 4-jaw self-centering chuck so there is minimal movement of the object to be centered. Then, slowly approach the object (midway) with the Alignment Tool while the lathe is turning at a very slow speed (25 rpm) or turn it by hand. Immediately after the Alignment Tool Bearing makes contact with object and turns without hesitation, the object should be centered and no further adjustment should be made. Tighten the jaws slowly. There should be no contact gaps on any of the jaws where they meet the object. If so, turn the object slightly and repeat the process.
You can see this and 66 other handy tips on the Sherline web site at www.sherline.com/pages/tips.htm.
Books and Videos for Machinists
Get advice on machining from some of the best around. Whether you prefer to thumb through a book or watch a video, Sherlineís book store offers a good selection to help answer your questions on metalworking. Books on woodworking are easy to find, but if youíve looked for good books on metalworking you know they are not so plentiful. Here are some of the ones we have found the most useful:
P/N 3050/3053óVertical Milling ColumnóWriteup $150.00
P/N 3050-CNC/3053-CNCóVertical Milling ColumnóWriteup† $235.00
P/N 3480/3485óDeluxe Vertical Milling ColumnóWriteup† $170.00
P/N 3580/3585óMulti-Direction Vertical Milling ColumnóWriteup† $375.00
Did you know?
ï Each month Sherline offers an ìInternet Specialî that saves you 20% on the purchase price of a selected accessory. To find out what is on special each month you have to visit Sherlineís site. To find the special, go to Section 2 of the main menu look for a link that says ìSave 20%.î
ï Sherline has not had a price increase since October, 2003!!!
ï Knowing how Sherlineís part numbering system works can make it easier to find what you are looking for. We have a page that explains the logic at http://www.sherline.com/partnos.htm.
ï Though Sherlineís instructions are the most comprehensive in the industry, there is only so much we can include with the products. If you want to go beyond what is in the instructions that come with your machines or accessories, Joe Martin has written a book that gave him 350 pages to expand on what he has to say about machining at the small end of the size scale. CLICK HERE to view a description of his book Tabletop Machining. It is now in its fifth printing and is not only informative, it is also a good read. 8.5 x 11î, softbound, full color.
Upcoming Model Engineering Shows
ï Estevan Model Engineering Showó
ï Western Engine Model ExhibitionóAugust, 2012,
Send us your show details and we will post them hereÖ
Joe Martin Craftsmanship Foundation News
ï New Exhibitsó
ï Club and Group VisitsóJuly 7th saw a visit from the North County Cruisers car club. On the August 4th, two car clubs scheduled visits at the museum. In the morning the Vintage Truck Historical Association visited the museum, and in the afternoon the Palomar Model A Ford Club stopped by, offering a free car show for other museum visitors. See the Club Visits page for photos of some of the participants.
ï Five more 6-foot glass display cases have been ordered for the museum as the number items on display continues to grow. If you havenít been in to visit in a while, stop back again soon and bring a friend. We are always adding to and updating our displays.