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Building the Infill Shooting Plane #7: Time to Tap

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Blog entry by JayT posted 07-30-2016 10:10 PM 838 reads 0 times favorited 8 comments Add to Favorites Watch
« Part 6: Mouth to Mouth Part 7 of Building the Infill Shooting Plane series Part 8: Doing some body work »

With the mouth cut, it’s time to start the metal work.

First step is to connect the two pieces of steel. Now, I don’t claim to be a machinist and there are likely better ways to do some of these steps. But I’ll post what worked best for me and you can change and adapt as your skills and available tools allow.

At the end of the piece of 1/8 steel, mark where you want to install the first machine screw. If you have layout fluid, that would be best. In place of that, I just marked over the area with a marker and scratched the lines through the black. Worked just fine.

I went about 3/4 in from the end and 3/16 up from the bottom in order to center the hole in the 3/8 base plate, scratched the lines with a marking gauge and knife and marked the point with an automatic center punch.

After that, both pieces were clamped to a squared up piece of scrap every which way I could and taken to the drill press with the appropriate sized drill bit (#25 for a 10-24 tap). If you haven’t drilled much steel, the best way I’ve found is to create a dimple using the drill bit dry, add a drop of light oil or cutting fluid to the dimple and drill some more.

Go ahead and drill through the 1/8 plate and dimple the 3/8. Using a squared up block clamped to the steel really helps stabilize it while you drill.

Then the 1/8 can be removed, a drop of oil added and drill down into the 3/8. Every 1/8-3/16, pull the drill bit up to clear chips and add another drop of oil. You’ll need to drill deeper than the length of the machine screw to allow enough room for the tap to work correctly and for chips to accumulate. While I’m sure there’s a standard formula for this, I just add 1/2 inch to the length of the machine screw and drill to that depth.

Note: When doing this, I decided that 3/4 machine screws were probably more than necessary and got some 1/2 inch ones instead. I’ve updated the first post of the series. You can certainly use the 3/4, it just means drilling and tapping more metal, along with the increased risk of breaking a tap.

So for my 1/2in machine screws, there is a 7/8 deep hole drilled into the 3/8 steel.

Now that hole can be tapped. As mentioned before, make sure to use good quality taps. Those you can buy at the big box or hardware store are fine for cleaning up existing threads or working with mild steel, but not the best choice for cutting new ones in tool steel. Take your time and go slow. Use plenty of cutting fluid, make sure to start the tap straight (make an alignment block if that will help) and reverse the tap frequently to break off the shavings. All tapping operations are time for patience—think tortoise over the hare. Impatience will probably result in a broken tap, followed by lots of cursing. (In case you haven’t figured out, breaking a tap sucks. I’ve done it three times and it’s a sinking feeling every time.)

I like to use a plug tap to start. It has a longer taper on the end that helps to get started straight. Every 1/8 to 1/4 turn, the tap gets reversed. When I feel it binding, it’s time to back the tap out and add some cutting fluid. Once the hole is well started, I switch to a bottoming tap. It allows cutting closer to the bottom of the hole, but with the sharper taper, is not the best choice for starting a hole.

Note: I had very good success this time switching back and forth between the plug tap and the bottoming tap. When the plug tap started to bind a bit, switching to the bottoming tap allowed it to cut the tapered threads to full depth without starting new ones. Once it started to get difficult, going back to the plug tap allowed it to just cut on the taper. This meant that both types were cutting less length at a time and therefore had less stress and were less likely to break.

Check frequently to see when you are at correct depth. Some people have feeler gauges for this, I just used one of the steel machine screws. When it goes all the way in, the hole is good.

Now the hole in the 1/8 plate can be enlarged at the drill press so that the machine screw passes through freely (for the 10-24, a 13/64 bit was the perfect size). Fasten the two pieces of steel together with the one machine screw and repeat the process at the other end. Mark, drill, tap, enlarge and fasten. Then the middle screws can be marked out . . . .

. . . . and drilled. With machine screws installed on both ends, you can drill through both pieces of steel at once. Here I have the steel clamped to two squared up pieces of scrap to help keep things lined up. The one in the back that cannot be seen is tall enough to support the side and base pieces.

Tapped and machine screws installed. Note that we’re still using the steel machine screws, as they will go in and out several more times, so you don’t want to mess up the softer brass ones. Save those for final assembly.

Again, go SLOW! I cannot emphasize this enough. While the earlier blog post about laying out for cuts took much longer to write than to actually do, this is the opposite. I’m sure someone with machine shop skills and tools could do this much faster and better, but this what I had to work with.

Now a very small countersink can be put on the holes-it doesn’t take much.

The best way to check is to use one of the brass screws and make sure that the bottom of the slot stays above the steel.

Once proper depth of cut is established, it can be set and transferred to the other holes. Reinstall the steel machine screws.

Next installment: Add some body to your work.

-- "Good judgement is the result of experience. A lot of experience is the result of poor judgement."



8 comments so far

View Don W's profile

Don W

17955 posts in 2028 days


#1 posted 07-30-2016 10:23 PM

Some more nice work JayT

-- Master hand plane hoarder. - http://timetestedtools.net

View JayT's profile

JayT

4772 posts in 1671 days


#2 posted 07-31-2016 02:48 AM

Thanks Don. It was blogs by you and Ripthorn that gave me enough confidence to try to build a plane with infill influences in the first place. After this one and a couple other projects are done, I’m looking to build a transitional infill smoother.

-- "Good judgement is the result of experience. A lot of experience is the result of poor judgement."

View ki7hy's profile

ki7hy

493 posts in 199 days


#3 posted 07-31-2016 04:23 AM

All I have is dewalt for taps…..sigh. Wish me luck. I’ll probably give it a shot tomorrow. Thanks again Jay.

View JayT's profile

JayT

4772 posts in 1671 days


#4 posted 07-31-2016 12:51 PM


All I have is dewalt for taps…..sigh. Wish me luck. I ll probably give it a shot tomorrow. Thanks again Jay.

- ki7hy

I’d strongly recommend ordering some better taps from wherever you got the metal and waiting until they show up. All the taps I’ve broken have been store brands. Using the higher quality ones this time, none broke. Some of that is probably more experience on my part and alternating the taps, but I think the bigger factor was quality of the tools.

If a tap breaks off and you can’t get it out, you’ll end up having to either scrap the base and start over or pay a machine shop to remove it for you. Another option would be to see if a machine shop would tap the holes for you. It’ll cost a little bit, but might save a lot more in the long run.

-- "Good judgement is the result of experience. A lot of experience is the result of poor judgement."

View duckmilk's profile

duckmilk

1660 posts in 784 days


#5 posted 07-31-2016 04:54 PM

Another option would be to see if a machine shop would tap the holes for you. It ll cost a little bit, but might save a lot more in the long run.

- JayT

Machine shop makes a lot of sense to me.
Backing up to my question in the previous installment, what are your thoughts about using a plasma cutter (guided by some sort of block) to cut the mouth in the 1/8 plate? I have a buddy who has one.
I really appreciate this series Jay.

ki7hy, I have not started on this project yet. I’m in the process of getting a floor put down in my shop. After that it will probably be a workbench build. Then, sometime after that, I’ll build one of these.

-- "Duck and Bob would be out doin some farming with funny hats on." chrisstef

View JayT's profile

JayT

4772 posts in 1671 days


#6 posted 07-31-2016 05:27 PM

Duck, when I did the first two, I asked a coworker about using his plasma cutter and once I explained the project, he didn’t think it was a very good idea. The problem that he saw is that the electric current finds its own way through the steel and would leave a very coarse and ragged cut. He thought a water jet would be a much better tool, but didn’t have one. Best analogy I can come up with is that using a plasma cutter for this level of work would be like using a chainsaw to cut dovetails.

If you have a good machine shop in the area, take them a sketch of what you want and see what they come up with. I’ve wondered several times if having a machine shop do all the metal work would be worth the money. It would certainly save on time and frustration.

-- "Good judgement is the result of experience. A lot of experience is the result of poor judgement."

View Don W's profile

Don W

17955 posts in 2028 days


#7 posted 07-31-2016 06:54 PM

I agree. A plasma cutter would leave a much to rough of a surface.

-- Master hand plane hoarder. - http://timetestedtools.net

View duckmilk's profile

duckmilk

1660 posts in 784 days


#8 posted 08-01-2016 02:42 AM

Thanks guys, it was just a thought. I have had sheet steel cut with one and it seemed to leave a pretty narrow and clean line, however this may be different.

-- "Duck and Bob would be out doin some farming with funny hats on." chrisstef

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