Tap Arm

[bmac2]

I had to think where to post this? Tools, Machine Modifications, Home Foundry & Casting Projects? In the end this is a casting project.

Whenever I finish a project with a lot of holes to tap I start thinking of making a tapping jig. After finishing Mr. Elmer Verburg #5 (https://www.homemodelenginemachinist.com/threads/elmer’s-5-geared-engine-maybe.30206/) with all those wonderful #2-56 screws I found myself once again thinking about a jig. I’ve seen a few where if you have a drill press with a round table you can just lift out the table and make a bushing that will drop in. Nice and simple, just make a bushing and a shaft with something to hold the tap on one end and some sort of knob on the other end.

A few years back I picked up this small drill press from Canadian Tire thinking it would be better than a hand drill and I wouldn’t be running out to the garage whenever I needed a straight hole. It’s turned out to be surprisingly good. The only change I have done was replacing the depth stop collar. It was plastic and just plain horrible but simple to make a replacement out of aluminum. Unfortunately it has a square table so no arm with a nice round hole to work with.
My wife has taken photography courses and bugs me if I have all my misc. pegboard hangings as a back ground. . . . . so white box background it is

 

[bmac2]

It came to me that it would be easy enough as well as handy to add an arm to the drill press column. The other benefit is it wouldn’t take up any of my very limited shop space. So the plan is to have it clamp to the column in the same way as the table and just swing the table under it when in use. A shaft with a chuck and small hand wheel will run in a bushing on the end. All I’d need is a short piece of pipe that would/could be made to slide on the rear column with a short arm. This would require welding and I have a small wire feed but I just haven’t ever used it enough not to suck at it. There isn’t anything critical here except keeping the two holes parallel so I thought the easiest way would be to make with a quick and dirty casting. I have no concerns about shrinkage so for all intents and purposes the pattern just has to provide enough material for machining.

 

[bmac2]

Here I could go on about how laminating up small pieces of wood is stronger than using two large pieces but to be honest I had a bunch of small stuff in my patterning bin and I was too lazy to move my car and drag out the table saw. This is a split pattern so I put newspaper on the centre lines of the blanks and then let the glue dry overnight.

I hadn’t used a wood lathe much since high school and I’ve only used this one a couple of times. Who dreamed up this thing? No power feed and you set your depth of cut by running your knuckle along a “T” bar . . . . really?

Once I got past the anxiety of approaching a rapidly spinning chunk of wood with a pointy metal stick I think I would have made my old 3 fingered shop teacher proud, I marked it to length, parted it off then turned the blanks for the bushing end and core prints. I found this little lathe at Canuk Tire on the clearance table (no box) and I sure don’t miss getting saw dust all over the metal lathe and everything else in the basement shop.

 

[bmac2]

After cutting the top web to shape and drilling the holes in the big end for the core prints I got the 3 pieces glued up and let it sit over night to dry. The newspaper shows up as a dark line in the parts so alignment is pretty simple.

Before splitting the pattern I drilled through the big and small ends for the pins that will align the two half’s of the pattern for molding. If you’ve ever bought a bookshelf from Ikea you have a bunch of these around and they make great locator pins.

The newspaper creates a weak spot in the glue-up making it easy to separate with a putty knife and maybe a light tap with a chisel to get things started. Then the draft angle was sanded in on all the flat surfaces. Sanding in the draft on the top web is a lot easier before the core prints are added.

The vertical web is made up of two pieces of 1/8” Masonite (hard board) just cut to size and glued into place.

Cut the core prints to length, sanded the draft angle into the ends, glued them into place and left everything to dry.

 

[bmac2]

Once dry all the inner edges where filleted with wood putty and sanded smooth then 3 coats of high fill primer followed by a quick coat of gloss.

 

[bmac2]

You may notice by now that pattern making happens at a snail’s pace. If you glue it, wait overnight. If you paint it wait overnight . . . .

I haven cast anything in about a year so needless to say my green sand was completely dried out and in desperate need of attention. Normally after reconditioning I like to let it sit for a day then mull it again before I use it but I wanted to see how the pattern would pull so I rammed it up and it looked good (enough) so I didn’t have to rework any of the edges.

I think my sand is a bit wetter than I’d like but I thought I could give it a try. That and hell I just wanted to melt something!

This is where I ran into a small problem. The core prints are 1 ¼” diameter and my plan was to use a green sand core. Trouble was I didn’t have any sort of tubing long enough in my scrap. I found an old sink drain in my “Plumbing Stuff” box but it was only 3” long and I needed 4. What I ended up doing was screw two pieces of 2x4 together and drilling a 1 ¼” hole on the centre line. I don’t have a forstner long enough so I had to use a spade bit. The hole was rough, ugly and unfinished but I just wrapped wax paper around the inside and rammed it up hard with a couple of pieces of wire in it for support (think rebar in concrete). The result looks more like something the dog left on the lawn but its solid and will make a hole. The rough looking area in the top right is just where I botched it up a bit cutting the gate to the riser. It looks bad but it’s solid and has a matching pattern in the cope (top half of the sand mold) so it’s all good. I also screwed up that sink bob on the left it should have been going up into the cope. Just not thinking and out of practice.

 

[bmac2]

I extended the risers to get a little more head pressure. The webs where ¼” before sanding in the draft angle and I was concerned it might freeze before the bushing end filled. It was when I knocked it out that I realised that the sink bob was upside down and way too small to have done anything. From the look of the surface my sand was a little wet and I’d poured too hot.

All in all it’ll work. I wasn’t expecting much for the finish, I’d used a bunch of risers and some cut off scraps and extrusion so it was a bit of a garbage mix.

 

[bmac2]

Got it clamped down and dialed in on the mill to bore the big end to 1.81 to fit he column and the small end to .75. The big end was just ugly to bore out, use soft gummy aluminum in your melt and you get a casting that’s soft and gummy to machine.

The bushing was a nice press fit, and then I drilled and tapped the hole for the locking lug and split the big end web.
Note to self: put a couple of slitting saws on the Christmas wish list, the ones I have are starting to get pretty dull.

Cut the shaft to allow around 2 inches of travel which should be more than enough and threaded one end to fit a small Jacobs chuck and the other to fit the knob.

 

[bmac2]

Now my game plan was to give it a good cleaning, prime it and then finish it off with a coat of black Tremclad/Rustoleum Hammered Finish. I love that stuff it hides a multitude of sins. It can even make my welding look respectable.
But Old Mother Nature has decided to be a hag and started with this crap last weekend (yes Sept 15). It’s been getting warm enough to mostly melt during the day but it just hasn’t stopped.

The high for today is 1 c so if this keeps up I don’t think I will get around to painting it until spring. Which roughly translate means it’s a little tap arm on my small drill press and I probably won’t paint it.

I think this is going to work out to be a great little addition in the shop. With the drill press turned sideways on the bench (I don’t have it bolted down) and the table turned to the side I have plenty of room to use the knob without hitting my knuckles on head. I might add a spring to apply downward pressure but I’ll wait to see if I need it.

 

[10K Pete]

Bob, you just caused me to 'slap my forehead'! I've been wanting a tap guide forever and haven't got round tuit. Mostly cause I hadn't hit on the right design details. Your guide is perfect! I don't have a foundry but I can fabricate. So consider your idea copied. I'll post when I have it, hopefully in a few weeks.

Thanks!!!
Pete

 

[Cogsy]

Whenever I see an excellent project like this it makes me want to try my hand at casting again. I'm not sure if that's a good thing or not...

 

[tjwal]

Bob
Nice project and great write up as usual.
I made a stand alone tapping guide years ago. I must say your casting looks better than mine.
I picked up a set of long tap wrenches at Grizzly. http://www.grizzly.com/products/Extra-Long-Tap-Handle-Set/H2721
The current price is about the same but mine was a set of 3. I used the smallest one in my tapping arm. Even it would be too big for a design like yours but it works great in a bigger arm.

No snow in Calgary yet.

Cheers

John

 

[bmac2]

Hi Pete glad you found it useful. I was kicking around fabricating it out of 1/8” plate and thick walled tubing with a small enough ID that I could bore them out to fit. I figured so long as I could bore the two holes without changing the setup in the mill they would be parallel and that’s the only thing that I thought is critical. I’ve got a small (heat settings? High/Low) 120 volt flux core setup and I know that my welds would be a mess on the inside corners of the vertical web. Between that and the potential for me to warp it into a pretzel by overheating it with great gobs of filler metal I just went for the casting. One day I will talk myself into going out there and just practice running beads but so far my Scottish DNA keeps kicking in and saying “Are ye mad? Think of the bloody power bill!” For someone that can actually weld it could probably be knocked out in a weekend . . . including paint! The pattern was 2 weeks of watching glue dry then a half hour of fun doing the melt and pour.

 

[bmac2]

Whenever I see an excellent project like this it makes me want to try my hand at casting again. I'm not sure if that's a good thing or not...

Thanks Al. It is a great tool to be able to pull out of the tool box from time to time. I enjoy it much more now that I finally seem to have my sand dialed in.

 

[bmac2]

John those look like a nice set. The snow stopped overnight and I think we hit 9 or 10 in the sun today so the white stuff is gone for nowJ.

I had been using this for tapping small holes. I made it from the largest of a set of three pin vises I’d picked up at Busy Bee tools. It has a spring plunger in the end that would go into the chuck on the drill press to keep pressure on the tap. The problem was that it was awkward to use and you fought the motor if you didn’t removed the drive belt. The metal is so soft that I managed to completely ware it out in a couple of years.

I got a chance to try out the guide today and if I was going to change anything it would be the time line and make it 10 years ago. I had some 3mm holes to do and the knob is big enough to work comfortable yet provide excellent feedback from the tap. Something I hadn’t thought of until I was using it was that I can use the drill press hold down clamp to hold small irregular parts securely in place while tapping.
By the way small pieces of vinyl flooring make great pads for clamps. Stop by any “End of the Roll” and if you don’t lock your car the salesman will fill your trunk with “free samples” and business cards .

 

[nel2lar]

Bob
You did a very nice job on the tapping arm. The complete write up was excellent and pics sweet as candy.
Thank you for sharing.
Nelson

 

[MRA]

I really like that - thanks for the write up. I do some casting (and cheat with oil-bonded sand) - I could have a go at that. And I happen to have a box full of pin chucks too

 

[johnmcc69]

Very excellent Bob! A cool project & great casting tutorial.

What did you use for aluminum?

John

 

[bmac2]

MRA oil bonded isn’t a cheat. I’d use it myself if I could get it locally and cheap enough. Most everything I’ve seen or read shows it can produce a casting with a very nice finish.

Hi John. Thanks I’m glad you liked it. I have a couple hundred pounds of my “Good” aluminum mostly heads, transmission housings, etc. and about another hundred pounds from rims and other previously cast stuff stashed in 60L Rubber Maid totes in the garage (man I hope my wife doesn’t read this). For things like this where surface finish, shrinkage and machinability aren’t critical I just throw in anything I’m sure isn’t magnesium or zinc.

This was about 40/60 cut off gates and risers and a bunch of stuff from the scrap bin under the lathe. It’s nice knowing that that last inch or so that was in the chuck will find its way into melting pot one day.

I’m not 100% sure but I think the arm could be fabricated using pins and something like JB Weld. No need for welding or casting.

 

[goldstar31]

I’m not 100% sure but I think the arm could be fabricated using pins and something like JB Weld. No need for welding or casting.

Way back in the the early 70's, George Thomas wrote in Model Engineer of his rather more sophisticated ' Universal Pillar Drill' which included a facility to drill, stake, rivet and lots of other things. It is now incorporated in his book 'Workshop Techniques'. which includes a blow to blow account of his small dividing head and also dividing in the headstock of various Myford lathes using the 60 and 65 bullwheels.
As the years passed, it was discovered that splitting the cast iron arms could result in 'nipping' and cotters were suggested.
However, in those days many of us were strapped for cash and fabricated machines were made! Mine was welded.

Again- and I wrote this up at least once here, I suggested that scrap conrods from small engines like the BMC A Series engines were a ready made source of arms.

I hope this information is of some interest

Norm