Angled Bearing surface

[BobsModels]

HI

I am building a Galloway and have a question about the machining of the angled bearing surface. The cranks' bearing mount is angled 30 degrees.

The trick is that the plane of the bearing surface must intersect the centerline plane of the cylinder and timing gear. That is the center of the crank. There is one spot in "space" where that plane will line up correctly.

To my surprise I cannot figure out how to find a reference that would allow me to cut to this plane. Setting up the casting for the 30 degree angle is no problem with my sine table. I have made many angled surfaces over the years but for some reason I just cannot see how to find a reference that will tell me when to stop. I can mark a dot on the casting at the intersection which is a distance up from the base and a distance from the center of the timing gear but machining to a dot or even a line is not very accurate.

I assume there is some trick to this that I am not seeing.

Thanks

Bob

 

[Dave G]

Hi Bob,
When I reach this point in a build, I always go through the same thoughts as you. Seems like there should be an easier way to locate the hole. I normally just ink up the side of the suface and scribe a line centered between the cap bolt holes and then after setup on the mill I put on my trusty magnifocusers, really helps to see, and locate by lightly touching the surface
with a center drill to leave a mark and then move the table if neccessary to adjust location. The parting line between the cap and the frame should be easy to see to locate from. If the hole isn't perfectly centered, it shouldn't have any ill effects
on the bearing. The greater concern should be squareness of the hole to the cylinder bore and frame. I think if done with care one should be able to locate within .005 inch location this way. After finishing this hole, it normally becomes the datum for all other operations following. I hope this helps but I'm sure theres a better way. Dave

 

[putputman]

Bob, when I work with castings I usually do a layout first to make sure all of the casting details are on location. Sometimes they are not. The next thing I do is machine the bottom surface to the proper location (x.000 from bottom surface to C/L of cylinder). Then I set up and drill & ream or bore the holes on the side of the casting that locates the gears and other details on the side.
I drill & ream a 1/4" hole where the crank is located. Next I will set up the casting at the 30 degree angle and machine the bearing surfaces down to .125" from the bottom of the 1/4 hole. You should be able to see all of this in the following post. Go down about 1/2 way thru the post to see the photos.
Hope this helps a little.

http://www.homemodelenginemachinist.com/index.php?action=profile;u=1989;sa=showPosts;start=90

 

[BobsModels]

Thanks for the suggestions. I am still not sure what I will do but it will likely be just scribing a line and
machining to it. Mount the bearing blocks and bore the bearing hole, and then all the rest of the holes at the same setting that need to be on center.

I failed to mention that the Galloway is the 1/8 scale. The amount of material from the top of the rough casting surface to the center point is about .020 , so the drilling technique will not work too well, but is certainly to filed away for future operations.

I will post some pictures over on the castings section when I get it machined

Bob

 

[Dave G]

After thinking about it for a while, how about this. I like to center my bearing holes with the cap hold down bolts. We used to use an edge finder on our jig grinders that was made by the famous Moore machine tool manufacturer. This edge finder was a 90degree angle piece with a hole in it. The hole was centered with the inside surface of the edge. Picture a thick piece of angle iron with a hole positioned on the top surface that is centered on the same plane as the inside surface of the angle iron. To use this edge finder you could drill 2 holes that match your cap bolt pattern into the edge finder, making sure to center the hole with these cap holes which will center your bearing holes with your cap holes. Bolt the edge finder to the engine frame using these holes, remove the cap first of course, then indicate the hole in the edge finder. This should put you on location. Centered with the bolt holes and on center with the cap-frame center line. The trick is to make your edge finder as precise as possible. The hole in the edge finder for indicating can be any size but should be smooth and round and for this I recommend boring. I know a picture of one of these edge finders would help alot but I don't have one at this time.
If needed I could make one and post the pictures. Let me know. Dave

 

[gbritnell]

Hi Bob,
There is no trick. The only thing you can do is scribe a horizontal line which is the centerline of the crank. Then set the casting on end and scribe another line from the head end of the base to the centerline of the crank. Now you will have to machine to the intersection of the lines. I just finished building the 1/3 Galloway and this is how I did it. (picture attached) I am now working on the 1/6 Galloway and have done the same thing. You can then wiggle the intersection to establish your centerline for machining the lock step for the cap.
One thing you might want to check is the width of the lock for the bearing cap. I found the 1/3 engine to be minimal so when I went to the 1/6 engine I increased that width so that when I machined for the bearings it allowed a little wider rib.
As I stated, I started out with the 1/3 engine and found quite a few drawing errors that have since been corrected. As I moved on to the 1/6 engine some of these errors and others have reappeared. Before you machine any parts double check the dimensions. One thing is the connecting rod. It is double dimensioned wrongly on both the 1/3 and 1/6 engines. The stack up dimensions from centerline to centeline don't equal the centerline to centerline dimension given. I assumed the centerline to centerline dimension was correct so I shortened the rod accordingly.
I also have the castings and drawings for the 1/8 engine but haven't looked at them yet. Having talked with Shelly and others concerned I suspect that there are going to be errors with these drawings also.
For anyone building a Galloway engine please contact me offline for any information regarding the correct dimensions for these engines. The new suppliers have spent good money (with me and others) to correct and update the existing drawings so that they can put out a better product.
gbritnell

 

[BobsModels]

All

As I mentioned I am doing the 1/8 scale Galloway. I did the ignitor first. The drawings were so bad I redid them in a 3D cad system. After getting it all to fit properly using section views in 3D I built a nice ignitor. I then proceeded to do the entire model in 3D, talk about the errors, but in reality having built models for over 30 years I do not think I ever found a set of drawings that did not have errors. And you do not really build to the drawings, you start a sequence that will require custom fitting at some point.

I have just finished modifying the cylinder drawings a bit so things fit nicely. On a model that small .040 makes a big difference.

Anyway, when I am done I was going to offer the entire set to the new owners if they are interested. I used this as my learning tool since for 28 years I drew everything on paper. If I had understood dimensioning concepts better I could have done everthing with symbols and changed all the drawings at once just by changing a scale parameter. I know that would not have really worked but would have saved a lot of time for different scales.


Again I will post progress on the casting site.

Bob

 

[gbritnell]

Hi Bob,
Using Cad is great for you and me because we have it and know how to use it but what about the poor fellow who buys the kit and starts to wade in and when he gets a bunch of bits and pieces made finds that they don't fit together? As I mentioned earlier I have redrawn the entire set of 1/3 drawings in Cad and have started making corrections to the 1/6. Another fellow who built the 1/4 had done the same thing and from what I hear he is finishing up on them and then they will be used with all the kits that are sold from hear out.
The sad part is that the originators of the engines wouldn't take the time to correct both the drawings and the castings over the time that they sold them.
I got so frustrated at one point I just shoved everything aside and worked on something else.
gbritnell