Tapping a bolt hole in cast iron. Pretty standard?

[Holbs]

With my home security events being all quiet since Jan, I moved my work vehicle out of my 2 car garage wood working workshop. And now it's time to reconfigure real estate in the shop so I can get back to my main hobby. No, it isn't Blue Iris & cameras like it has been for this past year But wood working!
I bought a new Sawstop cabinet table saw with 52" rails to replace my Delta Unisaw cabinet saw. But then I thought...why not keep the Unisaw for a dedicated dado/secondary saw? So I put then next to each other. Still have to align/coplaner the Sawstop to the Unisaw and outfeed table. I'll use a copule simple beam clamps to clamp the two saws together. However, will need to drill 2 holes into the Unisaw (white cabinet saw) to accept the black rails....and also I have a cast iron router table that goes to the right of the Unisaw which will need 3 tapped holes.
I have never tapped holes before. Is tapping cast iron pretty normal or are there any 'watch out for ....' gotcha things to worry about?

 

[Ssayer]

You didn't say the size. That said, cast iron taps like butter. It's also very soft. If you don't have tapping fluid, at least make sure you use 3in1 oil or the like while tapping. Taps 1/4-20 and smaller are very easy to break, so take care...

 

[Holbs]

You didn't say the size. That said, cast iron taps like butter. It's also very soft. If you don't have tapping fluid, at least make sure you use 3in1 oil or the like while tapping. Taps 1/4-20 and smaller are very easy to break, so take care...

hmm. the Sawstop bolts are M8 so am thinking to stay the same.

 

[sebastiantombs]

Use plenty of cutting oil. Don't be cheap with it and be easy with the taps like @Ssayer said. It might be worthwhile getting some real cutting oil rather than 3-in-1 or oils like that. Make sure you use the right size bit for the pilot hole and use lots of oil when drilling as well. Go slow, both drilling and tapping.

 

[Holbs]

Use plenty of cutting oil. Don't be cheap with it and be easy with the taps like @Ssayer said. It might be worthwhile getting some real cutting oil rather than 3-in-1 or oils like that. Make sure you use the right size bit for the pilot hole and use lots of oil when drilling as well. Go slow, both drilling and tapping.

that's what I have on hand. 3-in-1 "Real cutting oil". Suggested brands?

 

[sebastiantombs]

Whatever you can find as long as it says cutting oil for metal, not for aluminum.

 

[Holbs]

Whatever you can find as long as it says cutting oil for metal, not for aluminum.

gotcha. will visit HD soon

 

[tspevacek]

I have used the good ole Oatey from Home depot. usually located around the plumbing stuff. Brand is not important, its just used to lubricate and cool the surfaces as you drill and cut.
cutting oil

 

[Holbs]

I have used the good ole Oatey from Home depot. usually located around the plumbing stuff. Brand is not important, its just used to lubricate and cool the surfaces as you drill and cut.
cutting oil

does threading make the metal hot? You thread by hand and go sooo slow, though.
Plumbing dept...gotcha. thanks.

 

[sebastiantombs]

Hand threading won't make the metal hot but using oil can sure help make it easier and help prevent broken taps. They're a bitch to get out once they snap. Extremely hard and extremely brittle.

 

[TonyR]

I like to go in slowly a quarter turn, then reverse a quarter to let metal chips fall out, then go back in this time a half turn, reverse half turn to bring those chips out, then in three-quarter turn.....etc., etc.

For you perverts out there I'm talking about using a tap to thread a hole, OK ?

 

[Holbs]

was watching some tapping videos. I can see why to go in and then back out. To do a M8 x 1.25 hole, need a 6.8mm drill bit. Which I do not have Ordering one along with cutting fluid. I have a general $40 tap & die set but not the correct sized drill bits. I do not tap & die often (this is my first time) so didn't want to sink in $200 for a tap & die set.

 

[Holbs]

thanks guys. I was super skittish at tapping a hole in cast iron as never tapped any hole in my life (muhahah...haha..ha...umm...).
Cut through like butter. Don't think I really needed tapping fluid but did use it to cover all bases.

 

[Flintstone61]

somebody taught me to go 1/2 turn in, then 1/4 turn counterclockwise out, and when you get 1 revolution of the tap inside go 1/4 turn forward 3/4 turn in reverse to keep from cracking the bit and cutting nice threads.

 

[Holbs]

somebody taught me to go 1/2 turn in, then 1/4 turn counterclockwise out, and when you get 1 revolution of the tap inside go 1/4 turn forward 3/4 turn in reverse to keep from cracking the bit and cutting nice threads.

yea...I did something like that. Though I felt I could just keep going without backing out. But, again, to play it safe, I went 1/2 in then 1/4 out often with the tapping fluid.

 

[sebastiantombs]

The reason to use oil is that cast iron is kind of abrasive compared to even the junkiest steels. As long as it worked, that's what counts!

 

[Holbs]

Now that my security event has died down, I can get back into my wood working hobby that was on hold for 2 years.
Gots 2 x 8MP Dahua cameras in the garage at each end and will put my double boobie camera right above the table saws. That way, if ever I cut a finger off, I can show everyone in HD!

 

[LJR_2019]

Sawstop is badass. We used similar system on bandsaw for cutting meat in the steak industry. Saved a guy's hand, instead he only ended up with a little scratch.

 

[sdkid]

Sawstop is badass. We used similar system on bandsaw for cutting meat in the steak industry. Saved a guy's hand, instead he only ended up with a little scratch.

But did you have any 8mp Dahuas set up to capture it in 4K beauty???

 

[LJR_2019]

But did you have any 8mp Dahuas set up to capture it in 4K beauty???

Hell no. lol..