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Tapping cast iron

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waynemn

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#1
I have a piece of steel I want to attach to cast iron frame on my lathe countershaft.

Which way would be better, bolt going through-hole on iron piece and tapping for the bolt on cast iron or through hole in the cast iron piece and tapping
the hole in the steel part?

waynemn
 

kd4gij

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#2
Cast iron is easy to drill and tap.. So to answer your question witch ever is best for the application.
 

Bi11Hudson

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#4
A lot would also depend on the "width" of the casting as well. And how much force it has to carry. All of this depends on the size of the bolt versus the width, thickness, et al.
The last few times I did this, I used the fat part of a strip of bacon as the lubricant. There are a lot of good fluids out there, most illegal. Bacon was cheap, disposable, and in no wise related to anything but cooking. It works good, too.
 

Technical Ted

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#5
As in all things... it depends. In general, if everything is equal like thickness, overall size etc., threads in steel will be stronger than threads in cast iron because carbon steel is stronger than cast iron. Your question is too general without enough specifics to give a specific answer, but this is a guideline.

Ted
 

David S

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#6
I guess the other option if you are unsure and since you can come through from either side...it sounds. Then just put in a clearance hole in both pieces and use a nut and bolt. But I may not be visualizing your arrangement.

David
 

waynemn

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#7
I guess the other option if you are unsure and since you can come through from either side...it sounds. Then just put in a clearance hole in both pieces and use a nut and bolt. But I may not be visualizing your arrangement.

David
Hi David
Clearance hole in both pieces is a possibility. There is plenty of room.
waynemn
 

bfd

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#8
I would prefer to tap the hole in steel as it would be stronger and take a better load. also if you need to remove it and install it a lot I would do that better in steel bill
 

waynemn

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#9
I would prefer to tap the hole in steel as it would be stronger and take a better load. also if you need to remove it and install it a lot I would do that better in steel bill
Thanks Bill
That was kind of my thought also, wanted to kind of confirm it. It would be a one time attachment and do not foresee a need to remove it.
waynemn
 

NortonDommi

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#11
Tapping is fine but use a coarse thread. Whitworth was invented for use with Cast Iron. These days UNC or Metric coarse. Use a washer under the bolt head as well. Like with machining Cast Iron no lubricant.
 

Glenn Goodlett

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#12
I just had to drill and tap a bunch of small blind holes in a casting. I was deathly afraid of breaking a drill or tap off in the casting, so I used name brand American made drills and taps with tap magic in every hole and I didn't have any issues.
 

FanMan

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#13
I'd be inclined to drill the cast iron and tap the steel because the steel part is [presumably] easier to replace if the threads strip out or you break a tap.
 

Silverbullet

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#14
Cast iron will hold up as long or longer then steel when tapped , if it strips out a nutsert is an easy repair , just drill and tap the insert thread screw in and push the little pins in after screwing it in. Heli coil is another option. I've used both in all types of metal even spark plug holes.
 
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