Tapping small holes in cast iron

I guess I will probably be the dissenting voice in regards to keeping a machine 'pristine' vs modifying for current use. I understand the feelings about leaving a machine original. I have them too but they are not overwhelming. Look at it selfishly for a sec. It is a functional improvement that a new owner would be nuts to remove. Does one plan to sell the machine as a restored or restorable antique or are the plans to use the machine to the best of its capability for the rest of ones adulthood? If it is the latter, then the dispensation of the machine after one is dead is irrelevant. Modify. If that means holes, so be it.
 
I had no problem drilling and tapping my Chinese lathe to install the DROs. As for drilling an older machine, I personally would not hesitate. If I am using it as a machine to make things, then modifying it with improvements seems natural. If on the other hand I was trying to start a museum...
 
Bob Korves said:
Usually, Chinese imports not so much...
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Maybe closer to pig iron?

I never understood the extremist aversion to drilling a machine or modifying a vise. I know some guys seem to brandish it like a badge of pride, but ultimately its about getting the job done. Sure, I cry if the table on a mill gets dinged, or a mill slams into a vise due to pour programming, but it happens. I have 3 screwless vises semi permanently mounted on three of my machines, and they all have modified jaws so I can take advantage of the full working envelope of the machines.

My issue with Chinese cast iron is that with small fine threads it almost seems to crumble rather than cut. High quality machine taps seem to work better than hardware store plastic pouch hand taps or Chinese sets from the usual sources. A little lead in helps a lot. If you have enough depth (sometimes you don't) then you can clearance drill a short lead in to help guide the tap in straight. On steel or aluminum if you don't start the tap straight it will cut anyway. If its really bad you will break the tap, but it will cut right up until that point. With cast iron it will tap up until the cast iron gives effective stripping the hole. Get the tap started straight. Use quality taps. With the cast iron the chips don't clear very well even with a spiral flute tap. Take the time to clear the chips. Machine taps on average are better than hand taps, and just about any machine tap is better than a cheap import hand tap. Spiral point taps do seem to cut with less force than a spiral flute tap so if practical use them, but chip packing can cause the tap to stop and rip the threads from the wall of the hole. If trying to use them blind, back the tap all the way out periodically and blow the chips out of the hole.

~~ I see some guys were posting while I was off getting my coffee ~~
 
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Bob Korves said:
What about using Cyanoacrylate (CA, super glue) to mount the brackets to mount the scales to?
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I'd say first test a coupon on something sacrificial out of sight. Although there are opinions that CA is Loctite & vise-versa, I mess around with a lot of different CA's (different hobby). Some have similar properties, others are very different. With CA you generally want very good surfaces & even then, very little working time to position. With LT, especially like the ones engineered for larger gaps it might be a bit more forgiving & better end result. They have lots of spec sheets to refer to whereas CA is a bit more iffy depending on the supplier. LT also has accelerators (CA=kickers) and primers to promote adhesion

I guess on the future removable side, they can come off under shear like hammer whack. They also fail about their rated temperature. Clickspring uses this principle a lot to hold skinny awkward parts in fixtures to be turned on the lathe & then heated to release. But you are in a better position to assess, would this be a semi-sacrifical bracket or something where the scale itself might get abused in the process. The beauty of fasteners & shims using threaded posts is it can be knocked down & reconstructed again, which I have had to do on my machines chasing down another mechanical problem.

As an adhesive, epoxy might be another & better option. Even an off the shelf filled epoxy like JB weld will give you lots of working time, similar or better strength especially under vibration & shock, more forgiving of uneven or rougher surface. It also has a pretty decent shear force for removal but I would opt for localized heat. And consider that might be beyond the temp your paint cries uncle if its close by. I've heard of these specialized levelling/shimming epoxies for big boy machines which are no doubt engineered for that specific purpose. But goes to show you how composites can be integrated into 'metal' machines in the appropriate application.
 
I guess really , if you want dro on it or not. No matter which way you mount them. There's always going to be some damage at minimum gluing will mar or crack the paint , drilling small holes and tapping to me is the lesser of the evils. Tapped holes can be plugged and dabbled with paint . But the choice is do you want the dro or not. Mounting shouldn't be a problem if you want the machine to be more accurate.
 
Bob- got it- you really hate to deface the good machine. There has been a great deal of progress made in adhesives. This might just be the way to go. If you reverse course sometime in the future, a stiff rotary wire brush could be used for removal.
 
There has been great progress in powerful magnets...but alas not sure this would be an appropriate application.....or would it??

David
 
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Sorry Bob.... couldn't resist. I'll try to be more helpful in the future.

Ted
 
It's just a machine not a priceless historic artifact, drill holes wherever required.

Say this to yourself 3 times very slowly.

It Is Just A Machine
 
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