Holt 75 Crankshaft

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ddeal

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Hello folks, I just started to work on the Holt engine and I already made my first mistake. I drilled my centers in the ends of the steel rod slightly off and now there is about 0.005" of runout on the bar. This was partially due to the fact that my lathe chuck has about 0.002" of runout and I don't have a dead center for it. I'm thinking I might have to get one

My first question is, Is this a significant amount or can I ignore it and move on?

Secondly, if this is too much to ignore what is the best way to fix it? I already turned the outside to final diameter and one end to the final diameter so I can't just take a cut to true it up. I was thinking that if there is any room to play with on either end of the crankshaft I could just shorten it about 3/8" and drill a new center.

If this is unfixable it isn't a huge loss. The material wasn't very expensive so I could just start over.
 

dnalot

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You can make your own dead center for the chuck end by simply turning a piece of stock to a point. I don't think the run out will be a problem. The shaft could be shortened and the difference made up by making the flywheels a bit thinner or the fan pulley could be made with a little reach to extend it beyond the end of the shaft. . Could you provide photos of the ends of the material you have started to turn? It makes it easier to understand how you are going about supporting the material for turning the journals.

I have been looking forward to seeing other builds to George Britnel's drawings. The drawings are superb, I have found no errors thus far.

Mark T
 

ddeal

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These are the pictures I have taken so far. I have not started machining the journals yet. I have only finished one end of the shaft.

We have a different lathe that has a dead center but I'm not as comfortable with that lathe. I will probably end up using it though.

I did not think about making the flywheels thinner. I like that idea. You wouldn't ever really notice it.
 

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ddeal

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Well I got the problem all worked out and I finished the other end of the crankshaft. I put the bar in two v-blocks and spun it with an indicator. In the end I had less than 0.001" of runout. Time to figure out how to do the crank journals.
 

mfrick

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When making a dead center to go into the lathe chuck it is best to machine the end that goes in the chuck with a shoulder then chuck on that surface and machine the point on other the should prevents the center from slipping in the chuck when pressure is put on it from the tailstock and or machining. I then mark the dead center to register with no. 1 jaw then when I need it again I put in line it up and take light cut off to true it up.
Mike
 

ddeal

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Thank you for the advice. I now have another question. What tips do you all have when it comes to turning a crankshaft? I have been trying to think of what the best method would be to turn the journals without bending the shaft.
 

mfrick

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Well the best method that I have found that works for me is to rough out the journal area by sawing the excess material out then put a bolt with washers on either side to hold the area rigid while machining the other journal, then move the bolt to the newly machined journal and clamp then machine, I machine the journals first then the main shaft area.
Mike
 

ddeal

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I had thought about that. I was thinking I could mill away the excess and then insert spacers, but I was thinking that it would be really hard to make sure the spacers were precise enough to ensure the shaft would not bend at all.
 

mfrick

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So with bolts and heavy washers they clamp the two sides and limits movement and they stay in place not like spacers which have a tendency to fall out unless glued in.

Mike
 

ddeal

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Okay I guess we were talking about two different things. I'm having trouble visualizing what you mean. You wouldn't happen to have a picture would you?
 

gbritnell

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I made the spacers just a light push fit then put super glue around them. When they needed to come out you just give them a tap and they break loose.
 

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