Replies

1. 
   jeffn7 | Jun 13, 2003 09:02am | #1

   depends on how thick the cast section is, but drilling it isn't a big deal. Of course, getting the hold square to the surface is important because you are going to tap threads into it.

   There's probably some machinists here that will provide a more complete answer, but a regular drill bit for metal works fine. When drilling, spray some wd-40 to lubricate the bit, also go slow and let the bit do the work. Same for tapping the hole, use wd-40 for lubrication and by all means invest a couple of $ in a good tap wrench to go with the tap, it will make a difference. Let the tap do the work, it will draw itself in once it gets started.

2. 
   fredsmart48 | Jun 13, 2003 10:07am | #2

    

   CAUTION - taps are very, very hard and brittle will not take a lot of side pressure. If you brake it off in the metal you will need to get a carbide drill bit or diamond bit to drill it out.

   Taping treads are not hard to do but you do need to keep the tap parallel to the drill hole when you start.

   Next you start taping by pushing down on the tap with even pressure and turning it clock wise as you feel it bite the metal, advance it about 1/2 turn and then back it out to clear the waste. Then turn it in again until it bite and advance it another 1/2 turn and back it out. Keep doing that until you cut the threads all the way through.

    

   As for drilling a hole from the inside out that will depend on how large (long) your drill is or how large the hole in the table top is. Be careful how you hold the drill handle so you can release the trigger if the bit jams and twisted the drill in your hands you could damage your hand or wrist.

   You may be better off if you turn the saw upside down it may give you more room to work.

1. 
   forestgirl | Jun 13, 2003 07:40pm | #8

   Fred, thank you for the detailed description of how to tap.  That helps alot!  Thank you also for the reminder about not holding on to the drill too tight.  I've done this before -- ouch! -- and still can forget sometimes.

   The holes are going to be in the trunnion, not the tabletop.  Actually just realized I'm not sure if they're supposed to go all the way through or not.  It may not matter, but I'll see if I can take a look at the current JTS and see how it's done.  Thanks again.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

3. 
   Jeff | Jun 13, 2003 02:38pm | #3

   FG

   Cast iron is pretty soft stuff.

   Drills easy with a sharp drill and lubricant. WD-40 will do, but I like

   to use a drilling and tapping fluid called Do-Drill.

   I suggest starting with a small drill and working up.

   When you buy the tap and handle, be sure to buy the proper size drill to

   match.

   Tapping from the other side is fine as long as everything is long enough

   to go thru.

   Good luck.

   Jeff

4. 
   ToolDoc | Jun 13, 2003 05:21pm | #4

   Jamie: Hmmm sounds like you got yourself into a other fine pickle..<G>..so far you have gotten good advise from the other posters,I can only echo these thoughts use a HS reg twist bit no cheapie.. A quality made Tap  & use plenty of lube either cutting oil or Tap Magic or even WD40..when both drilling & tapping..keep your drill straight & tap straight.. I have faith in you your no Dummy there First Lady of the Forest.. Now Don't let the team down...

                        ToolDoc

5. 
   Len | Jun 13, 2003 05:39pm | #5

   Jamie,

   As said before drilling isn't a problem. Tapping will be difficult but not impossible.

   I would make up a tapping block. It's a block of metal, usually steel but aluminum works fine. Drill a hole the diameter of the outside diameter of the tap your using in the block on a drill press. The block should be tall enough to reach the shank of the tap so it's not wobbling in the hole. You can use maple or oak as well. It just doesn't last.

   Never tap with out cutting fluid. OSH carries it. I would use it for drill too. It's messier but works better. WD40 drys to fast.

   I would also use the same method to drill the hole too.

   Hope this helps,

   Len

6. 
   jimmyk | Jun 13, 2003 05:52pm | #6

   "Question is, how hard would it be to get a good hole drilled and tapped from the top-side of the table through the throat plate?"

   Don't know if that is possible, I know there's not enough room under my throat plate to do it, unless I crank it up to 45 deg. then maybe I can. Center punch where the holes should go first so the bit doesn't wander the drill a small hole then the final tap drill hole. Make sure you use a starter (taper) tap, it will help to line up with the hole better. And don't try using a crescent wrench to turn the tap, buy a small tap handle that will turn the tap more evenly instead of loading to one side and breaking it. WD40 works fine for cast iron.

   View Image  View Image

1. 
   forestgirl | Jun 13, 2003 07:44pm | #9

   Wow!  Lots of good info here this morning, but I'm supposed to be on the boat (ferry) to Edmonds, so gotta go.  Thanks everyone, will come back this afternoon and digest it all!  Have a great weekend everyone.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

7. 
   Andrew | Jun 13, 2003 07:26pm | #7

   First of all, let me make one thing clear, you DO NOT want to use any tapping fluid when tapping cast iron, despite what the others have said. You also don't need to use any coolant when drilling cast iron. I'm assuming you've never worked with cast iron before, but I have, and it doesn't make curly metal chips when you machine it, it makes powder, so all coolant does is make a huge mess that is hard to clean up. With any other ferrous metal you want to use coolant, but you will never see a real machine shop using coolant on cast iron.  

   I would not recommend leaving the trunion in place, seeing how this is your first time tapping a thread. First it will be very difficult to spot and drill the holes square, and you might end up breaking a tap off in the hole, or if you don't start the tap the right way, it will just enlarge the hole without cutting threads.

   You can use a regular steel twist drill for cast iron without any problems, just make sure that you use a metal punch to make a dimple where you want your holes to be, or the drill will wander around. Also, make sure that you use a drill bit that is the same size as the minor diameter of the thread. There are lots of charts that will tell you the proper size bit to use for any given tap size. I would also recommend practicing on a scrap piece of steel so you can get a feel of how to start a tap.

   Don't worry about having to realign everything when you take the saw top off. It's really no big deal, and you'll be able to do a better job drilling and tapping without it in the way. A big time saver when it comes to aligning the miter slots to the blade is to get them as parallel to the blade as you can, then you tighten up the bolts, and use a soft faced hammer (brass or plastic) to tap it into alignment. This way you don't have you worry about the table moving on you when you tighten the bolts.

   Hope this helps

   Andrew

8. 
   davearnone | Jun 13, 2003 10:58pm | #10

   More advice:

   Listen to Andrew.

   You do NOT want to break the tap.  The situation you describe is not a good situation for a first time hesitant tapper.  Odds are given a freehand, tight situation like this, unless the bolt size is large (1/4+) you will break it. 

   Remove the trunnion.  If you break the tap you'll be removing it anyway.

   Use a tapping block or better the drill press chuck and quill to guide the tap.  Turn it by hand with the power off.  Drill the hole with the trunnion clamped and then tap without moving a thing and you'll be a first time tapping champ!

   Fluid is not required for cast iron for exactly the reason Andrew describes.  Fluid will also make you more prone to mistakes cause its slippery. 

   Not required but if possible use a single flute spiral point tap.

   Feel is everything.  When the tap starts to bind, back up until the torque drops.  If you are drilling a blind hole be careful to not try and force the tap into the bottom of the hole.  It will break. 

1. 
   WorkshopJon | Jun 14, 2003 06:58am | #11

   "More advice:

   Listen to Andrew.

   .....Use a tapping block or better the drill press chuck and quill to guide the tap.  Turn it by hand with the power off.  Drill the hole with the trunnion clamped and then tap..."

   Good advice but, all (that I've ever seen) tap handles have a center countersink so that you can put a center point in a drill press after you drill the tap hole to guide it. No need to chuck the tap, way to easy to break it if you do that. On tapping cast iron....no fluids, just compressed air. BTW, easiest way to make a tapping block (for minimal use) is with a piece of wood and a drill press (crude, but it works).

   Here's a link to the company I work at. Most of the stuff on the site I have built or been involved on. After viewing, you will see I have tapped almost every mtrl. imaginable.

   Jon

   http://www.jppattern.com/

1. 
   davearnone | Jun 14, 2003 08:29pm | #17

   Good words Jon.  I agree.

   dave

2. 
   davearnone | Jun 14, 2003 08:32pm | #18

   Hey Jon.  I checked out your website.  very nice.  i especially like the tag line.

   cheers, dave

9. 
   forestgirl | Jun 14, 2003 10:02am | #12

   I continue to appreciate all the tapping info coming my way.  I installed the splitter tonight, rigging up a way to use just the one original mounting hole, but I still plan to get it re-mounted using the two smaller holes, which will give it more stability.

   Will print out all your responses and keep them for reference.  Will also be drilling holes in the cast iron wings at some point, so happy to learn about working with metal.

   Bedtime -- g'night!!

   forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

1. 
   Adrian | Jun 14, 2003 03:55pm | #13

   Agreeing with the guys that say no fluids for cast iron (not that I'm an expert, but the guys that teach other trades in my college here are, and they've corrected me on a couple of things I used to do, fluids/cast iron being one of them).

   Don't see how you could do a good job without taking the trunnion out.cabinetmaker/college instructor. Cape Breton, N.SWAY too conservative to be merely right wing

2. 
   trialnut | Jun 14, 2003 04:18pm | #14

   Forestgirl

   Since you allready have it mounted, if there is room, you may be able to just drill a small hole through the mounting bracket into the trunion and put in a roll pin. Do this with the splitter in place and lined up where you want it, just drill through both parts. This will keep it in position without the need of tapping a hole and if you are a little out of square drilling it will not be a problem.

   Keep us posted on the outcome.

   RichThe Professional Termite

1. 
   forestgirl | Jun 14, 2003 07:18pm | #16

   Thanks for the idea, Rich.  The working installation of the splitter does seem to open some other avenues, eh?  If I use a roll-pin, will I be able to later remove the bracket should I want/need to?  Do I drill the hole all the way through the trunnion?forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

1. 
   GHR | Jun 15, 2003 07:49am | #19

   I would tell you how to drill and tap, but you have too much conflicting advice already.

   This is a poor way to learn to a simple job.

1. 
   forestgirl | Jun 15, 2003 08:00am | #20

   It's OK, George, I will learn how to do it by doing it, but I'll wade through the information and opinions presented here to help me in my approach.  I'm pretty good at sifting through various instructions and opinions and deciding which ones seem to make sense, and then just giving it a try!

   Sounds like a couple of other people learned something new reading this thread too, so it's all to a good cause.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

2. 
   WorkshopJon | Jun 15, 2003 05:40pm | #23

   "I would tell you how to drill and tap, but you have too much conflicting advice already."

   George,

   Reading through, IMO she has good advice and bad. The purpose of a forum is for posters to throw in their two cents and share their experience (and qualifications hopefully for giving advice). You have not added anything.

   Cast iron is pretty easy to tap compared to nearly everything else. Forestgirl has all the info she needs now. BTW FG, on the off chance you break a tap, you can use a broken tap extractor to remove it.

   Jon

3. 
   forestgirl | Jun 15, 2003 09:08pm | #25

   Thanks Jon, I was a bit taken aback by George's "Hrumph" 

   Re: breaking a tap, I tend to go pretty slow on such things, rarely try to horse somethin' around when working with small tools, so I think I'll be OK.  Just don't get near me when I have a wrecking bar in my hands though!  Love tearing out sheet rock!forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

2. 
   trialnut | Jun 15, 2003 04:21pm | #22

   Forestgirl

   Yes, if you use a roll pin you will be able to remove the assembly any time you want.  If you can drill all the way through by all means do so. This will make removal easier as you can then just drive the pin out. Roll pins do not have the tendency to "get stuck" as they are nothing but a spring. With two pins you could remove it and put it back in exactly the same position, no realignment necessary.

   Drilling and tapping is not a difficult task but the roll pins would make reattachment easier and IMHO be easier to do to begin with. Just getting out of the box and tossing out other ideas.  If you do decide to tap, take the previously offered advice and practice on some scrap till you feel comfortable with it.

   RichThe Professional Termite

1. 
   forestgirl | Jun 15, 2003 09:05pm | #24

   Thanks Rich, I'm liking the idea of the roll pins.  Now that I have the splitter installed, it would be easy to get the holes in the correct place.  The one thing I'd need to check is whether or not there's enough "wiggle room" in the adjustment slots to line up for a blade that has stiffeners added to the assembly.  As long as there is enough slack for that, I could use roll pins instead of screws.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

3. 
   ToolDoc | Jun 14, 2003 05:55pm | #15

   Gee, even i learned something diffrent from this thread,as i always used cutting oil when I drilled or tapped cast Iron,reason being I figured that Heat & Friction plus stress are a Tap & twist Bits worist enemy soo I flooded it with oil,yeah it was a mess to clean up cause unlike steel you don't get nice swirls of metal from the bit just a pile of metal dust which creates a slushy like mix yuck.. but I never had bit or tap breakage a added plus in my book...

                                       ToolDoc

10. 
    fredsmart48 | Jun 15, 2003 10:39am | #21

    http://www.hosam.com/model/howto.html

     

    here is a web site the explains is some detail how to tap.   also the use of cutting fluid.