Author Topic: "Robby" a Novel Mill Engine  (Read 24634 times)

Offline Don1966

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Re: "Robby" a Novel Mill Engine
« Reply #15 on: September 09, 2015, 12:24:26 AM »
Tim I am pulling up a chair so bring it on. 


 :drinking-41: :popcornsmall:

Don

Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #16 on: September 09, 2015, 12:13:44 PM »
Dave, Achim, and Don, thanks for checking in!

Frame fabrication continues.

Three frame cross-pieces were sawn from a chunk of cold-rolled steel and milled to 1/4" thickness. All work to this point was done manually with the Bridgeport. The next shot shows the raw cross pieces roughly in position in relation to the side pieces.



It often happens that I get "into the zone" and forget completely about the camera. Such was the case when I shaped the front and mid cross pieces with a series of CNC operations. The large hole and the four cylinder mounting holes in the front piece were drilled and bored at the Bridgeport before the outside profile was done by CNC. The inside of the middle cross piece was CNC'd out.
The cross pieces were drilled and tapped for the 0-80 cap screws that will hold the frame together. The rear cross-piece still needs some sawing and shaping.


The pivots where the Robert's mechanism mounts to the front and mid cross pieces need to be accurately aligned with respect to each other. To maintain alignment while the frame is assembled, I connected the cross pieces with one long bar. Later, after the frame has been finally glued and screwed together, the pivot holes will drilled, and the middle of the bar will be sawn away.


Here's the frame fabrication after epoxy was applied and the screws tightened up. I'm sure JB Weld would have worked fine in this application, but I wanted to try a Loctite product "Epoxy Weld", which seems to work fine.


Thanks,

--Tim

Offline Tennessee Whiskey

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Re: "Robby" a Novel Mill Engine
« Reply #17 on: September 09, 2015, 12:19:01 PM »
Looks great Tim. Those 0-80's raise my pucker factor when tapping in steel.  :popcorn: :DrinkPint: and following along.

Cletus

Offline gbritnell

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Re: "Robby" a Novel Mill Engine
« Reply #18 on: September 09, 2015, 12:28:09 PM »
Hi Tim,
It looks like it's going to be a very unique engine. I'll definitely be following the progress.
gbritnell
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Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #19 on: September 09, 2015, 02:46:23 PM »
It's good to have you look in, George!

Cletus, affirmative on the pucker factor of the 0-80 steel tapping.

I need to mention that I have recently been trying out thread-forming taps. I bought #0, #2, and #4 for starters, and I did the tapping here with the the #0 thread-forming tap. Don't get me wrong, the experience in 1018 steel was still hair-raising, but it was done without any mishap. I don't think it would have gone as well or as quickly with the HSS thread-cutting taps I have been using.

I've also used the new taps in aluminum and brass with great results. I'm sold. You just have to be aware that the drill sizes are different (larger) for this type of tap.

--Tim

Online Dan Rowe

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Re: "Robby" a Novel Mill Engine
« Reply #20 on: September 09, 2015, 03:20:54 PM »
Tim, I have been using small form taps for a while now and I use a free smart phone app for my tap chart because the one on the wall has only cutting taps. I use a small tap stand and for tapping and I do not find myself holding my breath waiting for a tiny snapping sound.

I used a 0-80 form tap to thread a stainless steel part from Shapeways, which is something I would not have tried with a cutting tap.

Dan
ShaylocoDan

Offline Ian S C

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Re: "Robby" a Novel Mill Engine
« Reply #21 on: September 09, 2015, 03:41:36 PM »
Just been looking at my thread flow tap info, they suggest brass, aluminium, stainless steel, and LEADED steel, cast iron does not deform like other metals, and non leaded steel has too much friction.
Used in the right place they are great, and I feel I can tap with more confidence.
Ian S C

Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #22 on: September 09, 2015, 03:53:20 PM »
Glad others have found success with these taps. I'm pretty sure Stan S. uses them too.

Yeah Dan, I found the drill sizes somewhere on the web, and penciled in an extra column on my wall chart.

I almost always tap now using a guided tap wrench with the guide either in the mill spindle or the lathe tailstock.

A wrench like this:

http://www.mcmaster.com/#tap-wrenches/=yv3ory

--Tim

Offline mklotz

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Re: "Robby" a Novel Mill Engine
« Reply #23 on: September 09, 2015, 04:16:53 PM »
In my DRILL program, I use the following equation to find the tap drill for thread forming taps...

TD = MD - 0.0068*DOT/P

where:

TD = tap drill size
MD = major diameter of thread
DOT = desired depth of thread expressed as percentage
P = pitch of thread expressed as tpi

For example, a 1/4-20 thread with 75% DOT yields:

TD = 0.25 - 0.0068*75/20 = 0.2245"

Closest conventional drill is 5.7 mm but a #2 is close enough.
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Regards, Marv


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Online Dan Rowe

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Re: "Robby" a Novel Mill Engine
« Reply #24 on: September 09, 2015, 04:19:53 PM »
For those who always are searching for the calculator in the shop here is a printable tap chart for roll form taps:
http://balax.com/catalog/thredfloer-taps/ansi-thredfloer-hole-size-chart

And the metric version:
http://balax.com/catalog/thredfloer-taps/metric-thredfloer-hole-size-chart

Cheers Dan
ShaylocoDan

Offline mklotz

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Re: "Robby" a Novel Mill Engine
« Reply #25 on: September 09, 2015, 04:29:16 PM »
For those who always are searching for the calculator in the shop here is a printable tap chart for roll form taps:...

Who needs a calculator?  Do it in your head.  :)
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Regards, Marv


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Online Dan Rowe

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Re: "Robby" a Novel Mill Engine
« Reply #26 on: September 09, 2015, 04:54:25 PM »
Marv,
If I can not find my phone/calculator I use the simpler rule of thumb found in the MSC catalog, Tap Drill Size = Major Diameter - (Pitch / 2).
The formula you gave is listed just below the one I just wrote.

I have been using the cutting version of the simple fromula for years because it was too far to walk to find a tap chart on most ships.
For cutting taps Tap Drill = Major Diameter - Pitch

Cheers Dan

Edit: I should point out that the formulas I stated use the pitch exprssed as the distance form one part of the thread to the next identical part or for imperial the pitch is 1/TPi. Metric is simple just use the numbers on the tap.
« Last Edit: September 09, 2015, 05:22:43 PM by Dan Rowe »
ShaylocoDan

Offline nevadablue

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Re: "Robby" a Novel Mill Engine
« Reply #27 on: September 09, 2015, 08:51:10 PM »
I'm pulling up another chair for this show.

Offline Ian S C

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Re: "Robby" a Novel Mill Engine
« Reply #28 on: September 10, 2015, 01:05:23 PM »
Thought I should put up the BA Threadflow chart.
Ian S C

Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #29 on: September 10, 2015, 01:15:51 PM »
Dan, Ian, and nevadablue, it's great to see you watching. Also Cletus and Marv, I appreciate your further comments. With so many fine modelers watching, the pressure is on. I trust no one will hesitate to make suggestions or point up any blatantly stupid moves on my part.

The crankshaft will ride in plain aluminum bearings which are part of the fabricated frame. At the Bridgeport, a chunk of aluminum stock was drilled with countersunk holes for mounting to the frame, and also undersized holes for the crankshaft.


At the CNC mill, the first bearing block was screwed to a sacrificial plate which had been drilled and tapped to match the frame mount holes. A series of roughing outline passes proceeded, followed by a finishing pass at full depth.



The second bearing block blank (which was separated from the first by the roughing passes above) was attached to the same tapped tooling plate holes and the identical programs run again.


Here are the bearing block pieces ready for mounting, and then glued and screwed to the frame sides.



Now the bearing caps could be sawed off at the Bridgeport. Here I realized that pre-drilling the crankshaft bores was unnecessary and silly, but not a show stopper. Life goes on.


With the bearing caps now screwed on tightly, and the frame mounted on an angle plate, I drilled and reamed the crankshaft bearings.


In the same angle plate setup, I drilled the pivot holes for the Roberts linkage and also side-milled the front plate where the cylinder will mount. These crucial elements will now hopefully be square to each other.
The linkage pivots were supposed to be centered on the bar, but you can see they ended up low. The holes are located properly relative to the crankshaft though, so somehow the bar ended up a little high. Not perfect, but again not enough to stop the show.


Thanks again for watching,

--Tim