Tapping Wood issues

[Christopher K. Hartley]

Hi everyone it's been a while but I need some help. I'm trying to finish my vacuum chucks for small boxes and I decided to use wooden plates to hold the chuck cylinder. I started with maple using a tap purchased for the job I also am using a tap guide and a paddle bit 1/8" smaller than my 1 1/4" tap. Here are the issues I'm facing:

• First, the paddle bit (used on my drill press seems to make less than the perfect sized hole. I finally changed to an old adjustable wood bit and get a cleaner cut but still wonder why the paddle isn't working as well
• Second, The tap seems to cut away the threads as it is making them. I have tapped metal for many years and had no problems but the wood doesn't seem to react the same. Is it wood type, grain direction or what.

Any help would be appreciated. Thanks. By the way Merry Christmas and a Happy New Year to all.

[Thom Sturgill]

I would never trust a paddle bit to make a clean hole, not what they are designed for. They are designed for speed where looks are not important such as drilling holes in studs to run cable. Buy a forstner bit.

What tap are you using? The Beall taps are specifically designed for wood. Yes grain can be an issue. I use CA glue to stabilize the wood and have had success with MDF. Apply before and after the first pass and run a second pass to clean it out. This will also help air leakage as the end grain can act as straws to suck in air, so make sure that use a wood sealer. Tight grained maple is not too bad, but I have to soak MDF with shellac or other sealer.

[David Gilbert]

I have a Beall tap that is similar to yours, 1 1/4 x 8, and haven't had any problems. I also have a smaller 3/4 x 6 tap that I have used for making clamps and other tools. I always use a Forstner bit for my holes. I think the spade or paddle bits tend to wander and flex so they aren't as consistent. I always cut my threads across the grain of the wood. Trying to cut threads on the end grain creates very week threads that will almost always break.

Often I use a lubricant like mineral oil or a Danish oil when I am actually cutting the thread. If I am making a chuck for my lathe, I mount the wood in a scroll chuck and drill and then tap it right on the lathe. I use the tail stock to hold the tap and then a wrench to screw the tap into the wood. As it goes in, I crank the tail stock in to keep it aligned. After I have tapped the hole I coat it with CA glue to provide some extra hardness to the threads.

I have made a variety of vacuum chucks with this technique. Although MDF can be easily tapped, I haven't been that happy with its ability to allow air to leak through. My best chucks were made from some scrap phenolic polymer blocks or from laminated hard board. My wood chucks (beech and maple) seem to leak more than I think they should.

I hope this helps and good luck.

Cheers and Happy Holidays to all!
David

[Roger Chandler]

I would use a forstner bit Chris.......then apply CA glue to harden the threads once made, then go back after the glue dries and tap once again........this procedure has worked for me several times. Thom is correct about the beall taps.....they are made for wood.

[Dick Mahany]

All good advice so far. I typically use a forstner bit and a Beall tap and have excellent success with Maple and European Beech. I have also used the CA followed by a second "clean up" tap and it worked vey well.

I also tried tapping some 3/4 x 10 threads for auxialliary chucks for my live center with a conventional 3 flute tap and have less than good results. I can get enough thread to use, but found that a significant amount of the thread chipped away with the conventional tap. One thing that worked a little better with the conventional tap was to use a light hollowing cut after the forstner bit to open the hole diameter slightly. That produced a less chippy thread, but still didn't compare to the Beall cut thread.

[Christopher K. Hartley]

Thanks Guys, I had not thought of the CA but when you mentioned it I thought of my CEPS from the Rot Doctor. I used it on my boat transom and floor; it is an outstanding product. It will also help with the vacuum sealing issue. I am using a Beall tap and have fabricated a handle to turn it. The grain direction is helpful I was doing it wrong. I will also leave the paddle bit for other projects as you suggest. Thanks so much.

[David DeCristoforo]

Over the years I've threaded a lot of wood. I have not yet tried hand chasing fine threads on the lathe but I have used a number of different wood tap and die sets. Some of the things I learned:

The wood you use will have a lot to do with how well your threads turn out. Hard, dense woods work better than softer woods. Ring porous woods like oak or ash can be especially difficult. But brittle woods (like ebony) can be just as difficult to thread. the very best wood I ever found for threading is cocobolo. It has just the right combination of hardness and suppleness and the oily nature of the wood aids is cutting very clean threads. It is also important to select as straight a grain as possible. This is one place where figure is not beneficial!

Tapping into end grain is almost a fools errand.

When threading metal, the common practice is to back the tap off frequently to clear the waste. This also works with wood but you have to be careful that the tap is kept vertical. Otherwise, the cutting edges will break the threads. Or worse, the tap can "crossthread", ruining the work.

The drier the wood, the harder it is to get a clean thread. You can lubricate with wax or try to harden the wood with CA glue. But the best thing I found was to get the wood wet. After drilling the hole, I stop up one end with clay and fill the hole with water. Leave it to soak in for a few minutes and you will find that your threads are much cleaner. Plus the tap will cut much easier. Of course the water will swell the wood and after it has dried, it will shrink again possibly causing the threads fit to be a bit on the loose side. But this never seems to be extreme and wood moves so much with the seasons that threaded parts fit differently anyway, depending on the humidity.

Whether or not you wet the wood, use plenty of wax to lubricate the tap or die.

Cut a small chamfer on both the top and bottom of the entry hole before tapping.

[Jim Underwood]

Tapping into end grain is almost a fools errand.

To expand on this, if you tap into end grain you're chopping all the wood fibers in two. If you tap into side grain then you have a much better chance that the fibers remain intact lengthways and will hold up much better instead of breaking off.

If you absolutely need to tap into end grain because of grain orientation of the work piece, one solution I came up with was to turn the piece in such a way as to be able to glue a side grain piece onto a tenon or recess, and then tap that.

[Leo Van Der Loo]

To go in another direction, if you want to reuse these pieces often, then maybe a insert would be a better way to go ??

Fit something like this into the chucks and you can tap and reuse them many times, it should/could also reduce the leaking of the chucks, just a thought

reducer.jpg

[Faust M. Ruggiero]

I used stacked Baltic Birch for my vacuum clamps. I drilled the hole with a Forstner bit and threaded with Beall tap. After tapping, I soaked the tapped threads with thin CA. My chucks are a couple years old and still work well. However, If I make another, I may sink a 1 1/4" x 8 nut into the chuck. These are available from our favorite hardware supplier, Mc Master Carr.
faust

[Christopher K. Hartley]

I'm not sure if this topic has been covered before but this is a wealth of great info.I wonder if it should be a sticky for quick reference. Thanks to all of you, this is much appreciated.

[Thomas Canfield]

I have made quite a few jam chucks/plates out of MDF using the 1 1/4x8 and 1"x8 Beal taps. I drill with a Forstner bit and apply a liberal coat of 1#cut shellac and then retap. I have also made some 3/4" x10 (or whatever the standard 3/4" thread is on the Oneway live center) using a 3/4" bottom tap purchased from McMaster Carr. The bottom tap was chosen since the 3/4" ones are blind and the bottom tap works to provide the full thread with a shorter drilled hole. I use the shellac to harden the threads because of cost and ease of using.