Build - Finger Engine

Finger Engine Build - Improved NAMES Plan

[Dec. 5, 2014]

[Dec. 16, 2014 - modifications]

[Dec. 17, 2014 - added crank ratio information]

This finger engine was originally built based on the NAMES plans (see link information below), but later modified to improve operation. In fact, the revised engine works so much better, that I would urge anyone making an engine from the NAMES plan to make one simple modification, as explained below.

Links to Plans and Information

For links to plans and other information on finger engines, see below. As explained below, I made modifications to the original plans; accordingly, I redrew the entire plans, and these revised plans are available at the links below.

• General information : click on this link and scroll down to "finger engine". Note that the second "information" link includes discussion which alleges that the crank ratios for the NAMES engine are not correct and that this leads to difficult running.

• Revised plans in LibreOffice Draw format : https://drive.google.com/file/d/1g3lV1xXC7WcvYp0sc5y7-xmgeyuZ6Aa2/view?usp=sharing

• Revised plans in PDF format : https://drive.google.com/file/d/1mMPvfsik1b5DUgY9pgXPj-i5JqopvgaD/view?usp=sharing

Since I already mentioned the discussion on crank ratios (see comment above), and since I already drew up the diagram, I thought I may as well include it here:

https://drive.google.com/file/d/1Y_HDPUdMJbRb-Js61P7tAY_BtLxPkZ9ySw/view?usp=sharing

The Flywheel

To make the flywheel I used a slice of a metal cylinder I picked up at a garage sale. The metal was marked "Nichromaloy" on one end - other than that it is mystery metal. I cut off a slice using my portable bandsaw stand - it took about two minutes to make the cut in the approximately 3" diameter cylinder. The metal machined fairly well with what I would call an "OK" finish - good but not great. To get it nice and shiny, I finished up with emery cloth starting with 80 grit , then 180, 120, 240, and finally 400 grit to get an almost mirror finish.

I machined an "indented" section on each side of the flywheel, marking out the sections with Dykem and a digital caliper. I also drilled the center hole and finished up with a reamer. I opted to go with a solid flywheel both for a clean design, and also to keep as much flywheel weight as possible (although adding cut-outs would likely make a negligible difference).

The Post and the Flywheel Shaft

I opted to make the post for the flywheel wider at the base than at the top, both for appearance sake and for more stability. Instead of just making a simple hole for the flywheel shaft, I made a bearing sleeve out of bearing bronze and fixed it in place with a shrink fit; I made the bearing sleeve longer than the width of the post so that the ends of the sleeve would act as "washers."

The flywheel shaft was straightforward - the only significant difference from the plans was to mill the flat instead of filing it.

There are no specific pictures for this section, but other pictures on this page should show some of the relevant detail.

Lever and Finger Tab

The dimensions for the lever were marked out using Dykem; note that required holes were drilled/tapped and drilled reamed before milling to final shape. Note also that the original plans were modified to include a "cut out" for the finger tab. In addition, instead of mounting the finger tab with screws from above, through holes were drilled in the lever, and holes were drilled/tapped in the bottom of the finger tab. After final milling, the lever was finished up by polishing with a deburring wheel.

A "finger indent" was made in the blank for the finger tab by pocket milling a "rounded rectangle" section in the top using a rounded end mill. This was finished up with some final shaping using a Dremel grinding tool, finsihing up with emery cloth. Note also that the corners were rounded by marking with a radius gage and then hand filing, followed by more emery cloth polishing. The final result was worth the effort - the finger tab not only has a pleasing look, it has a very nice "feel" when operating the engine.

The Connecting Rod

The connecting rod was fairly straightforward, or should have been if I didn't have an "Aw $#!I!" moment (see picture far right below). While rounding the end of the piece in the mill, I inadvertently allowed it to go into "climb milling" mode - the mill pulled the piece out of my hand and milled a gouge in the side in the blink of an eye. Of course I already knew that when milling with this type of jig, one should only mill in "conventional" mode but it only took a split second of inattention to have to re-learn the lesson the hard way.

Odds and Ends - Washes, Screws, and Base

Instead of using brass washers as called for in the plan, I made Teflon washers using this method. I made the brass shoulder screws on the lathe, using a die to do the threading; to slot the screws I used a slitting saw in the mill, holding the screw with a collet block. I made the screws with a 0.120" head thickness, and slotted 0.060" width to a depth of 0.060".

The base was made from red oak (4" x 5" instead of 5" x 5", since that is what I had in the shop). The edges were chamfered on the table saw, and the oak was finished with two coats of clear wipe-on polyurethane.

NAMES Finger Engine Plans Revised

Initially I made the finger engine essentially according to the NAMES plan, with some minor modifications. The engine did operate, but it was difficult to keep it going, and it took quite a bit of practice even to accomplish that. Subsequently, I ran across some discussion (see links section above) which indicated that the original NAMES plans are not optimal. I experimented with various small changes, and found one simple change which made a very big difference in ease of operation of the engine: Change the crank radius from 0.250" to 0.350". This simple change makes the engine much easier to operate, and does not require any other significant changes (however, I also otherwise modified the crank as shown below).

As a side note, I also found that increasing the length of the connecting rod also improved operation. However, making a significant change in this regard results in the lever hitting the base, unless the lever is also significantly modified (or alternatively, the post is made longer). Further, changing the connecting rod length does not improve operation as much as changing the crank radius. In the end, I settled for modifying the crank, but I have no doubt that this engine could still be improved in other ways.

The Crankshaft

[Revised Dec. 16, 2014]

For the flywheel I changed the crank radius from 0.250" to 0.350" - as noted above this change alone improves operation. In addition, I redesigned the crank to be heavily counter-weighted; based on a comparison to a simpler "test crank" I made earlier, I believe this change also leads to improved operation.

The revised crank was made from a piece of cold rolled steel, milled down to 0.250" thickness; this blank was then drilled for the crank and shoulder screw. The next step was to drill and tap for the set screw - the tap is too short to tap the blank fully, but it does tap it to a sufficient depth that the tapping can be completed after final milling. After completeiong of drilling and tapping, the shape is marked out with layout dye and rough cut to shape on the bandsaw.

The rounded sections are then milled using the same jig as was used to mill the ends of the connecting rod (see picture above). Due to the hardness of the steel as compared to aluminum, the piece was milled using very shallow cuts of no more than 0.003" depth of cut. Also, since the piece was so short, an adjustable wrench was used on the opposing end to provide better leverage and control.

After final milling, the "corners" where the straight edge meets the curved section were gently rounded with a file. Finally, the entire piece was smoothed with emery cloth followed by a final polishing with a deburring wheel. The completed crank can be seen in the pictures at the top and bottom of this page.

The Completed Engine

Three more views of the completed engine are shown below.