# How Would You Center This Under The Spindle?



## tomw (Feb 14, 2016)

Dear All,

This is a continuation of this thread.

The project is to build steam engine #5 from PM Research:




The part I am currently working on is the main frame. The drawing is below.




All the circled dimensions are high tolerance.

Here is a shot of the part during machining the top bore and it's relief:




My question, now more broadly defined, is how would you go about centering this:




under the spindle to machine the inner surfaces of the journal bosses.

The inner distance between boss surfaces has a tolerance of  ±.005, and they need to be square to the crank axis. See this drawing below:




I have already machined the central bore and relief on the top of the frame (bottom in the set up picture above) and the crankshaft journals. My goal is to use that bore plus the crankshaft as a reference to machine the inner surfaces of the crank journals.

So, hints, tips and tricks will be much appreciated.

And, the winner gets a prize. Not from me, mind you, but if you live long enough you eventually get a prize.

I am missing something, that I know. Unfortunately, it is a known unknown of an enigma.

Thank you all for your help and suggestions.

Cheers,

Tom


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## stupoty (Feb 14, 2016)

If you make a plug for the bore with a big flange of a reasonable height under it and stand that on the mill table you might be able to get an indicator mounted in the spindle to sweep around it.

Stuart


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## tomw (Feb 14, 2016)

I forgot to mention, I am using a Sherline 5400 mill with an extended column. Small is beautiful, I am told regularly. Probably because I am overweight.


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## Billh50 (Feb 14, 2016)

I would have made a plug that fit the bore well and had a flange to clamp to the table. Then if I did not have enough travel to get an indicator down to the plug to center it. I would make a rod to lower the indicator enough so I could. Then put the part on have at it.


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## stupoty (Feb 14, 2016)

Billh50 said:


> I would have made a plug that fit the bore well and had a flange to clamp to the table. Then if I did not have enough travel to get an indicator down to the plug to center it. I would make a rod to lower the indicator enough so I could. Then put the part on have at it.



If their was a hole in the centre of the top hat type plug , that could be held with a t nut and indicated and the part mounted on the upstand of the top hat.

Stuart


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## chips&more (Feb 14, 2016)

As said, use a plug for center. Use a drill blank and indicator for square. And use an adjustable parallel and micrometer for measuring the 0.880”…Dave


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## Billh50 (Feb 14, 2016)

If you make plug put a center hole in it as well that fits a pin snug. That way you can use the plug with pin to locate center when part is laying down for any side holes just by indicating pin center.


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## tomw (Feb 14, 2016)

All great suggestions. 

I did make a plug and pin to bore to find the center of the journal bores for the crankshaft. I just can't find a way to indicate from it when vertical.

​

If I make a plug that is tall enough to be both reached by an indicator, and have enough room around it to sweep, the plug will interfere with the milling operation. Unless I am not understanding what folks are suggesting. Which is likely.

The piece is a little over 7 inches tall, and the bore through the top is 3/4". The journals are about 7/8" from the bottom. The area available to sweep an indicator becomes small quickly below that point.

However, based on your suggestions, I am thinking of doing the following:

1) make a tight fitting plug with a concentric flange that just fits inside the recessed area. The flange will be about 1/8" thick. This is like the plug pictured above, but with a much shorter flange and without the long pin.
2) center drill a clearance a 10/32 SHCS hole in the plug
3) mount the plug to a tooling plate, mount the plate to the mill table
4) indicate in the plug at spindle center
5) mount the frame onto the plug and get it all square and level. Then clamp the whole thing securely (somehow).

Would this work, or would I introduce way to much slop?

BTW, I earlier stated the tolerance for journal to journal incorrectly  It is .01, not .005.  I didn't understand my notes. Sorry.

Thanks,

Tom


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## Billh50 (Feb 15, 2016)

If the plug has a rim or through hole to hold it down then you indicate the plug before mounting the part. The part is then not in the way and will be on center of the plug when put on plug and clamped down. Once you have the part clamped on and squared up then you can mill the other end to the print because you are on center of the parts bore. Squaring the part up is a simple matter of indicating the edge of the part in the x, y direction. Just remember to set dials to O before moving table. If you can't indicate the part with indicator in spindle then indicate it to edge of the table. This should get it straight enough for milling.


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## Billh50 (Feb 15, 2016)

to indicate along edge of table for squareness use the indicator holder shown below.


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## TommyD (Feb 15, 2016)

Are there any target points anywhere on the plans? Target points establish datum points, primary, secondary ant teriary to fixture castings. I used to work in a shop where we dis a lot of machining from castings.

http://www.meadinfo.org/2009/05/datum-targets-gd-better-understanding.html


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## Moparmyway (Feb 16, 2016)

Billh50 said:


> to indicate along edge of table for squareness use the indicator holder shown below.
> View attachment 122240
> View attachment 122241


I have this tool, but I have no idea how to use it or what it is used for
Would you be willing to provide a link or a quick how to on this tool for me please ?
Thank you Billh50 !!


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## Billh50 (Feb 16, 2016)

ok.....push the 2 pins down and hold those against the edge of the table. This allows you to slide the base along the table while pins stay against the side. This will allow you to indicate the side of the part parallel to the edge of the table. So pick the flattest or longest side to indicate. You should then be able to mill the top because know center and now have a side that is straight along the axis.


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## tomw (Feb 16, 2016)

Dear All,

Success! And Failure! 

Using the approach I wrote about above:



tomw said:


> 1) make a tight fitting plug with a concentric flange that just fits inside the recessed area. The flange will be about 1/8" thick. This is like the plug pictured above, but with a much shorter flange and without the long pin.
> 2) center drill a clearance a 10/32 SHCS hole in the plug ...



I was able to get everything square and centered relative to the upper bore.  Yea!!!

Unfortunately, it became evident upon milling the journals that my bore was not centered along the crankshaft axis.  Boo!

The casting that I received was not perfect, the two halves of the castings were shifted relative to each other. Somehow, in trying to correct for this, I ended up about .070 off center. 

So, I ordered a new casting and will try again. Total cost of the mistake is a weeks worth of evenings and $22.

I also ordered some extended drill bits to make it easer to drill the crankshaft journal caps and base mounting holes. 

If folks are interested, I may do a build log. Let me know.

Cheers,

Tom


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## Billh50 (Feb 16, 2016)

It is always best to blue up the casting and lay out things before any machining. Also best to take your time and make sure you start off right. It is too easy to end up off somewhere without lay out everything first.


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## stupoty (Feb 17, 2016)

tomw said:


> If folks are interested, I may do a build log. Let me know.



Always good to see a project coming together 

Any chance of braze filling the casting to have a second shoot at it ?

Stuart


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## Moparmyway (Feb 17, 2016)

Billh50 said:


> ok.....push the 2 pins down and hold those against the edge of the table. This allows you to slide the base along the table while pins stay against the side. This will allow you to indicate the side of the part parallel to the edge of the table. So pick the flattest or longest side to indicate. You should then be able to mill the top because know center and now have a side that is straight along the axis.


Thank you Sir !


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## Billh50 (Feb 17, 2016)

Always try to help......I have used this method several times for 1 off parts.


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## Billh50 (Feb 17, 2016)

For 1 off parts with draft angles I use this method and line up the indicator to scribe lines as best I can by eye.


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## kvt (Feb 17, 2016)

It is nice to see you doing this one   I'm still working on my #7.   I wound up getting a new base cast for my #7.   The fun part is now ensuring the wholes in the cylinders line up with the new cast when I drill it.   Will have to work at it.      I agree with the blue up and marking things up  to start with.   In fact I have been putting the blue down,  then mark it real light,   Then If I want to change I just put a little more blue then redo it.  and measure and see if things line up until I get it right.    Again nice to see you working on this one.   How is it to do on the Sherline.


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## tomw (Feb 17, 2016)

kvt said:


> It is nice to see you doing this one   I'm still working on my #7.   I wound up getting a new base cast for my #7.   The fun part is now ensuring the wholes in the cylinders line up with the new cast when I drill it.   Will have to work at it.



Was the base poorly cast? I take it you mean the mounting holes? Ouch. The cylinder mounting holes are threaded. Have you considered using blind hole transfer punches? At least that is what I call them. You would also need a jig.



Billh50 said:


> It is always best to blue up the casting and lay out things before any machining. Also best to take your time and make sure you start off right. It is too easy to end up off somewhere without lay out everything first.





kvt said:


> I agree with the blue up and marking things up  to start with.   In fact I have been putting the blue down,  then mark it real light,   Then If I want to change I just put a little more blue then redo it.  and measure and see if things line up until I get it right.    Again nice to see you working on this one.



I'm not sure where bluing would have helped. I missed the bore by using the casting core, which was distorted, as my starting point. I think using some other reference point would have been great, I just couldn't figure out which or what or what have you.  But I obviously was missing something. Any help will be appreciated.



kvt said:


> How is it to do on the Sherline.



It is a challenge for me. But, I have been machining for almost a year. Another couple of weeks and I will have a year under my belt.

I think anyone familiar with machining and Sherline sized equipment should have no problems. 

Thus, I am f***ing doomed.

Cheers,

Tom


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## Billh50 (Feb 17, 2016)

Tom.....you might want to read the article in the link below. It was done by someone who machines small castings from kits.


http://www.schsm.org/html/machining_small_castings.html


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## kvt (Feb 17, 2016)

Your not doomed.   I am,   Ive been working on my #7  since about a week after you started yours.   Here is what I did on my second base cast,    Took at look and did some measures.  Then figured what I wanted to use as a starting point In my case Flat base. and approx. center of bore for crank rod.  Blued it all up and marked it out,   Then shimmed the base and cut it flat.   Also then shaved the front side of the base flat so that It gave me a squared reference point.   maybe that would work,  That was why I blued remarked, a few times till I could get what I wanted.   that saved me, as then all was easy to line up after that.   Seems some of their castings line up nice and some not as good, but isn't that whey they always make castings oversized.


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## Billh50 (Feb 18, 2016)

kvt is right about castings. Many castings are all over the place with locations but usually have enough stock to make the part intended. There are castings that are called Investment Castings. These are so close that very minimal machining is usually required. But they are too expensive for normal use. That is why it is usually best to blue it up and lay out everything before machining. Then decide how you want to machine it. Sometimes the first thought is not always the best. So run through the machining in your mind before you start. Sometimes it is better to just clean a surface, leaving it heavy just to hold the part for machining and then go back and finish that surface. The surface does not even have to be cleaned up completely as long as you have enough surface for holding.


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## planeflyer21 (Feb 18, 2016)

Even with production investment castings, variations from batch to batch.  Made for some real challenges when cutting cast 17-4 stainless valve bodies, when the portion of the body we had been using to mount to the fixture came to us in tolerance but larger than the steel fixture used for machining them.

I have to say, the work done by members here on rough castings is quite impressive!


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## tomw (Feb 18, 2016)

Thanks guys.  Until my new frame gets here, I am moving onto the cylinder. Looks simple.  Hah, as my latest thread indicates.

Tom


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