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Gerrit's Eureka Relieving device build

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gerritv:
It is fortuitous that Bjorn posted his build thread recently. I am in process of building a Jan Ridders Glass Cylinder engine and it requires T2.5 timing pulleys. I am not fond of spending money (it is a hereditary thing I think) so I intend to make my own pulleys. Originally I was going to use the fly cutter technique but with the tiny tip size I am concerned that the tool will not last cutting 3 pulleys.

So, I need to make proper cutters and then relieve them. As Duplex states in his original article series in ME 1949, more teeth is easier on the machine. Not wanting to cave in and use the alternatives, I need a relieving device. I researched a lot of patents, including the Hendley cross slide version but it turns out the Eureka is more feasible with the tools I have. I found Balzer's original 1895 patent for a previous version of the Eureka but the article I am basing this off is from the Centennial ME archive.

Off to the metal pile to find the chunks of steel from which to carve this thing. I opted to make the anchor and ratchet plates first so that the mandrels can be turned for a good fit. Not having a large boring head I bolted the 2 plates together after laying out and drilling a .125 guide pin hole in the centre. This was mounted in the 4 jaw and centred on the hole. A boring boring operation later and I reached the 1.500 dimension.

Off to the bandsaw for some rough trimming and then to the horizontal milling machine for cutting the  slots and cleaning up the straight bits. The round portions were trimmed on a belt/disc grinder and filed to the lines.

steamer:
Cool!    It's on the list..... 8)

watching along! :popcorn:

Don1966:
Great start Gerrit..... :ThumbsUp:


Don

gerritv:
Feeling confident, I started on the main mandrel. This lump has 2 eccentrics and 34 diameters, of which 2 need some accuracy. The eccentric offsets also need to be accurate otherwise the relief won't be enough (or too little) and the ratchet mechanism won't index properly.

Having only metal that is too big by a margin, it was first a tedious turning exercise. I started using a carbide insert tool so that I could take .010 cuts to get the majority of the metal off. I then offset the lump 0.168, checked that several times and finished the 1.75 and 1.500 main diameters. The 1.500 was finished to a what turned out to be .004" loose fit :-( Whoopsie 1 of more to come.
The mandrel was re-centred and the 1.000, .620 and .375 sections were turned. All fine so far except the slightly loose fit above.
Then came the time turn things around and to offset the other eccentric, which determines the amount of relief. This was turned to 1.12 to be held eventually in the 3 jaw when using the tool. I also drilled the centre hole for the small end, around which the tool will oscillate. I checked this offset 5 times, perhaps in hindsight I should have only checked 3 times! After finishing this section I did some checking and found I had offset in the wrong direction! Good thing I had made that 1.12 as I had enough to turn it correctly and down to 1". Also off course I ahd to remove the incorrect centre hole from the small end, also feasible since I had left this longer than needed.
And then it happened, the cutting tool dug in and up popped the work piece. I though all was fine but realized after some other checking that the .375 portion was bent. It now sits on my desk as a paper weight!

gerritv:
Having learned in life that learning is a good thing, I did a deep think about how to make this mandrel manufacturable. A fascination article from WWII on making the Bofors 40m anti aircraft gun ready for mass production came to mind. I also wanted to avoid producing another 5 lbs of swarf.

The result is to make the mandrel in 3 parts: the main eccentric with 0.168 offset, the main shaft with 0.030 offset and the small 0.375 shaft. this would assist in making adjustments later as well as reducing the risk of mistakes. And even better, a lot less cutting.

This resulted in proper parts and dimensions. The 0.375 hole was reamed with a .374 machine reamer, the resulting fit on my drill rod is great. I marked the 4 quadrants on the back of the main eccentric to assist in lining up with the main shaft later on. I still need to drill and tap a few set screw holes for the eccentric and the small shaft. The eccentric will also be glued using Weicon green retaining liquid (this is an affordable alternatie to Loctite, less than half price for same specs)

I also single pointed the 1/2-40 tpi thread although later realized that I should have ground the cutter at 55° instead of 60°. I turned the spindle by hand, not used to running the spindle in reverse with tool upside down yet ( a method that avoids the threading to a shoulder risks.)

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