Drilling and tapping shaper table for accessories: How to?

[David Stone (CT)]

I need to drill and tap a series of holes in the top of a used PM26 shaper to mount aftermarket guards and a stock feeder. My only experience of drilling into cast iron machines came in connection with attaching Unifence and Biesemeyer rails onto saws--and that didn't require much precision or any tapping. So basically I am coming at this with no background. I don't want to remove the top for the machine and am envisioning--correctly??--an approach using a portable drill and guide blocks to establish the correct hole pattern/spacing and keep the bit perpendicular. Guidance, advice and/or links to good threads or videos would be much appreciated.

[Jim Becker]

Drilling cast iron is actually pretty easy. The starting point is where you need to focus a bit of your energy because the better you mark and punch your center, the better the end result. A magnetic portable DP would be amazing for this job, but you can do good work with careful layout and center punching. And creating a guide block isn't a horrible idea, either!

[Bill Dufour]

Tap it dry, no lube of any kind.
Bill D

[Bruce Page]

As Jim said, drilling cast iron is not hard. If not already known, measure the bolt circle/pattern and make a matching drill template out of something flat like MDF. Place, carefully mark and punch with a center punch. Drill with steady pressure at a slow to moderate rpm. I generally drill CI dry but you can use simple motor oil as a lubricant. (messy)

[Tom M King]

The easiest way is with a magnetic drill press, if the top is thick enough for it to get a good bite. You didn't say where you are, but if you were close enough, I would loan you one.

I don't understand the recommendation to tap dry. I always use Dark cutting oil for drilling, or tapping cast iron. You can buy the dark cutting oil in the plumbing aisles of the big box stores. The dark cutting oil has extra sulfur in it, and is designed especially for drilling, and tapping cast iron.

You can't tap stopped holes with the drill press though. For those, you need a set of three taps, with the last one being a bottoming tap. I had to retap some holes in a tractor block up to 1", for holding on the loader frame.

You don't need to use a tap wrench. For those large holes, I ended up using 8 point sockets, and breaker bars. I bought some large tap wrenches off ebay, thinking that was what I needed, but couldn't get a full swing on the tractor. A ratchet will work, but with a breaker bar, you can go back, and forth easier.

Good quality cast iron, as I expect that machine top to be, is easy to thread.

[Sam Puhalovich]

David ... what the experienced guys ... all good answers ... did not mention is tapping technique. Use a guide to keep the tap vertical. Start with about 3 turns ... pushing down ... to engage the tapered part of the tap. From there-on, it's ... 1/2 turn 'forward' ... 2 turns 'back'. When you turn 'back' you'll feel a a burr break.

[Alex Zeller]

Cast iron basically turns to powder when drilled or tapped. Before buying the tap you need do some quick research as to what size drill bit you will need to match the tap. From there it's easy. Often with cast iron I'll just tap it without stopping. With steel you'll want to go forward for a 1/4 to a half turn then reverse. If you do use lubrication (I don't always) then you'll need to clean the threads of the tap after each hole. A guide would be nice but as long as you are careful it's not needed as long as you can hold the tap straight when starting to tap the hole. The only guide I have fits in my drill press so it's useless for something that can't be taken to the drill press like a table top. Just remember that cast iron to keep the dust out of everything. If it get's on metal to metal surfaces it'll work it's way in between them and wear things out.

[William Hodge]

I need to drill and tap a series of holes in the top of a used PM26 shaper to mount aftermarket guards and a stock feeder. My only experience of drilling into cast iron machines came in connection with attaching Unifence and Biesemeyer rails onto saws--and that didn't require much precision or any tapping. So basically I am coming at this with no background. I don't want to remove the top for the machine and am envisioning--correctly??--an approach using a portable drill and guide blocks to establish the correct hole pattern/spacing and keep the bit perpendicular. Guidance, advice and/or links to good threads or videos would be much appreciated.

I have mounted stock feeders on cast iron tables with through bolts, when the bottom is open. I use 7/16" holes and 3/8" bolts. The bolts then seat flat on the stock feeder
base. With real metal working tools, I could drill holes square to the table. With a little hand drill, that won't happen.

Also, drilling holes for jigs in the miter bar slot, if possible, saves having rough surfaces crop upon the table.

[Mike Kees]

I second what William says in the post above me. Unless your machine has a table that is 3/8''thick or more on the flat it is better to drill and run the bolts thru and just use a washer and nut.

[John C Bush]

Hi David,
I drilled and tapped thru holes in my TS for a stock feeder and it was easy to do. Check for webbing on the bottom of the table-- I positioned the feeder so the holes would miss any webbing. I didn't use oil for drilling and did for tapping. My tap and die set is a cheapo and the socket bolts I used seemed a little sloppy but hold just fine. I would get a better-more precision??- tap if I were to do it again. I used the feeder base to punch hole positions and made a guide to keep the drill vertical. Hardest part was getting the courage to punch holes in my new SS table!! Good luck.

[Ken Combs]

edit: can't post a pic

I've a tool similar to this for years.https://sawmillcreek.org/image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wCEAAkGBxMTEhUTExIVFRUXFRcYGBgXFxcXGBcYGh0XFxcYFh 0YHSggGB0lGxgXITEhJSkrLi4uGB8zODMsNygtLisBCgoKDg0O GxAQGi0lHyUtLS0tLS0tLS4tLS0tLS0tLS0tLS0tLS0tLS0tLS 0tLS0tLS0tLS0tLS0tLS0tLS0tLf/AABEIAQ0AvAMBIgACEQEDEQH/xAAcAAABBQEBAQAAAAAAAAAAAAAFAQIDBAYHAAj/xABCEAACAQIEAwUFBQcCBQUBAAABAhEAAwQSITEFQVEGEyJhcT KBkaGxUnLB0fAHFCMzQmKy4fEkQ4KSohY0c4PSFf/EABoBAAIDAQEAAAAAAAAAAAAAAAIDAAEEBQb/xAArEQACAgEDAwQBAwUAAAAAAAAAAQIRAxIhMQQFQRMiMlFhFC NCFVJxweH/2gAMAwEAAhEDEQA/AOtbERVob1EU1qTNtQ0aHuKxpwfSomeq1zEwKlkULG8SsZxpy3/KktGB6VJYuSN6ix0ZSRuPgRz3oXtuMX9oD7RYwBDrqQY91cj4V fvXbrXBqmcwPKdK2vH8X3iMAftAQfI/mKGdiMEpw6dSNfU0zDFSuxfVTeNJIbx3hwxGGcTLlTodx5 frXJuEY5rTZTqs6r59R0Nd5xOAjlWM4p2Cs3GLWi1pySdPGpJ/tYyPcab6VcGV59S9wBS GEqZB/UVWvNcotd7JvhgWfELl6BD4o6yYHrrQ1MQska6defmKJp1uCmn wUShnWvXDA5USKg1H 6A 6hosGQzGBoOtQWsBnYzog1Y Q5epP0ozdthQYjoOpJ0AHvodfcxkDaDcDXMev66ChaCTKuNxRu EBZW2uirtAqqLE1dFo 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And, to aid in starting the tap, it can be chucked in the tool also. You can't really tap it very far, but can at least start it straight.

Locating the holes to match the add-on fixtures is a whole 'nother issue.


I need to drill and tap a series of holes in the top of a used PM26 shaper to mount aftermarket guards and a stock feeder. My only experience of drilling into cast iron machines came in connection with attaching Unifence and Biesemeyer rails onto saws--and that didn't require much precision or any tapping. So basically I am coming at this with no background. I don't want to remove the top for the machine and am envisioning--correctly??--an approach using a portable drill and guide blocks to establish the correct hole pattern/spacing and keep the bit perpendicular. Guidance, advice and/or links to good threads or videos would be much appreciated.

[Erik Loza]

Thought: Not sure what the ribbing situation is like on the underside of your cast iron table but what if you through-drilled rather than tapping? Then, you wouldn't have to worry about alignment.

Erik

[Mark Bolton]

Another vote here for drilling through holes and not tapping unless your table surface is very thick. Most machines that come with tapped holes for feeders have boss's cast into the underside of the top to support the thread engagement. Holes in a thin top for fences and light accessories may not be an issue but you get a feeder loaded up or bound up out on the corner of a thin table and youll possibly blow the corner of the table off or blow the tapped holes right out of the cast iron surface.

We put a feeder on a slider that had no tapped holes and we punched clearance holes for the bolts and mounted a steel plate under the table permanently attached with the tapped holes so the bolts drop clear through the cast iron top and thread into the steel plate. That way we dont have to fuss around with nuts/washers/plates when we pull the feeder.

Have a band saw with tapped holes in a thin top and it alway gives me the willies when we mount a feeder on it and Im very careful not to heavily load the feeder for fear of blowing out the table.

[Andy D Jones]

Couple of thoughts...

I would check with a local tool-rental place about renting a magnetic drill (press). They are tailor-made for this job. They are expensive to purchase, so seldom worth buying if you only need it for a single job or two.

With regards to tapping technique, the forward then back (to break the chip and keep it from fouling the next flute) is not required if you use spiral taps. They are more expensive that straight-flute taps, but are much quicker to use, though I doubt it would make much difference in this application in cast iron.

As mentioned, those portable drill guides can also be used, after a fashion, as a tapping guide, to keep the tap normal to the table surface. Even if precision location is is not required, a tilted, threaded hole can cause an attached piece to loosen (or tighten) depending on which way the lateral load pushes on the tilted fastener.

-- Andy - Arlington TX

[Jim Becker]

edit: can't post a pic
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[Roger Feeley]

I was taught (back in 1974) to always machine cast iron dry. The instructor said something about oil making the iron harder. I’ve never had any problems because the stuff machines really easy. But I always wondered why.

[Mark Bolton]

I was taught (back in 1974) to always machine cast iron dry. The instructor said something about oil making the iron harder. I’ve never had any problems because the stuff machines really easy. But I always wondered why.

Cast iron machines so well dry because of high graphite content formed in the casting process.

[Tom M King]

Here's the 1" threaded hole in the tractor block. It originally was 3/4". It got messed up when the 3/4" bolt sheared off in it. On the other side, I was able to get by with one step up to 7/8".

Below those big holes were originally 5/8" threaded holes. I was able to clean up one of them, but the other three had to be upsized to 3/4".

Cutting the 1" threads, I used a 24" 1/2" drive breaker bar. It was pretty hard to cut. I'm not sure if the oil mattered, or not, but I was scared to try it without it. It still took quite a bit of effort. The 7/8" hole was noticeably easier, and the 3/4" threads cut like butter.

Here's the 1" hole. It came out perfect. I think it just has stuff in it in the picture.

That tractor would have been almost useless, if I hadn't been able to get the sheared bolts out, and remount the loader.

I bought that magnetic drill press just for that job. We tried drilling them with a 3/4" drill motor, but bent bits. I bought the drill press off ebay for about half the cost of a new one. I figured I could resell it, when I got through with it, for about what I had in it. I like it so much, that I decided to keep it. It's a monster tool!!

[David Stone (CT)]

Thanks for all the excellent advice so far. The suggestion to simply bolt on the feeder makes sense--as luck would have it, there is a rib in the general vicinity but I'm hopeful I can work around it. I think I will tap for the guards as they'll need to come on and off and I don't relish the idea of an arrangement where I've got to get inside under the hood to access the nuts.

[Tom M King]

I bought sets of individual sizes of taps, used off ebay, and only older, made in the USA brands. They all worked just fine.

At first, I only bought the large sizes that I needed for that tractor work. I liked them so much, that I went back, and bought sets of three in every size from 1/4", up. I had the standard set of taps, and dies, but didn't have the plugging, and bottoming taps. I didn't get a single set off ebay that wasn't ready to use.

[Jeff Duncan]

Lots of good advice already given. I've drilled and tapped dozens of holes for various machines over the years and will tell you once you've done the first one.... your realize theres not much to it. While I'm sure specialty equipment may be handy in certain situations, it's not worth it here IMHO. If I have to drill and tap a shaper top for example, grab the feeder base, mark out the holes and use a punch to get a nice precise starting point. Then I grab my cordless Makita to drill the holes and use my taps, (of unknown Asian origin), to tap them and done. You can use oil to tap but don't need it and it just makes it messier IMO. Cast iron is just really easy to drill and tap.

As for top thickness, my machines were generally of substantial size so usually no worries about top thickness..... though it is a good thing to keep in mind. Through bolts can work if needed, but its a lot quicker and easier if your top is thick enough to do without. I had through bolts for my table saw feeder and that was always a royal PITA to get setup:(

good luck,
JeffD

[Mel Fulks]

Yep. Agree with Jeff. Some never notice how soft the tops are .....but just wonder why dropping the the wrench on the
table always leaves dents !!

[Tom Bender]

Let's back up to your layout. I would do a careful layout on paper. Maybe with drafting tools, maybe with CAD. This will work better than just trying to lay out on the cast iron. Tape the paper in place and center punch.

Now for the drilling and tapping, like so many other things, practice really helps. You might even practice your layout. The second one should come out better and you can overlay them to see if they are the same.

I like the idea of a separate plate underneath with nuts welded on so you don't have to tap anything and the strain on the top is minimized.

If you decide too bolt thru, and you have the table off, you can fill some areas with auto body filler so your bolts or plate have good bearing.

[Chris Fournier]

No need to overthink this task. No tool rental required. As has been mentioned use the feeder base to layout your holes, avoiding ribbing. I make size on centre punches but you don't need to be that accurate as the bolts are undersized. Good centre punch to get started. Use your tap drill bit to drill through a square block of wood, say 2" thick. Now you have a guide to keep you square. Drill holes. Use your guide to start your tap, no lube needed in cast iron, it drills and taps like a dream. You'll be done before you know it.