I recently acquired my second metal shaper. I sold my last one quite awhile ago, though, and forgot whatever shaper skills I had. I decided to figure out how to make tee nuts on my shaper (I don't have a mill at present) and to make several sets of tee nuts, improving my procedure as I go. This piece is the result. If I did my technical writing job correctly, and if you follow my method, you will make tee nuts accurately and correctly on your shaper.
I do make certain assumptions. I'm assuming if you're reading this, you are familiar with machine tools and safety, for example. I'm also assuming you know how to grind high speed steel tool bits, and how to put work in a vise on parallels the correct way. Also, I assume you know about roughing and finishing, depth of cut and setting cutting speeds and stroke length and position.
Also, I'd like to pass along some wisdom I learned from experience. It's very easy to make mistakes when measuring and machining tee nuts. I very carefully measured the tee slots on my German drill press, for example. I made a sketch and dimensioned it carefully. Yet when I started making its tee nuts I realized that somehow I got several of the dimensions wrong. So I suggest you do sanity checks all throughout the process. If you're careful, you won't get bit the way I did. Also, it's super easy to put the part in the vise with the wrong side up and if you do that and start cutting you've scrapped the part. So keep your thinking cap handy and pay attention.
To my knowledge there is no standard terminology for the parts of a tee nut. I have chosen names:
Begin by measuring the slots for which you want tee nuts. Don't assume they are all the same, because sometimes they aren't. It may be helpful to use telescoping gages, as they can be easier to manipulate than calipers. One general note about tee nut dimensions - it's usually OK if you make the part a bit undersize. But there are a few exceptions. You want the tongue to fit the slot closely; i.e. be as big as it can be without binding. That way you can drill and tap for as large a fastener as possible. Also, you have to leave the top of the tongue a bit shy of the top of the slot. If the tee nut were flush with the top of the slot it wouldn't clamp correctly. Finally, if the base height is cut shorter than the base part of the slot, the amount that it is shorter has to be smaller than the amount the tongue is short of the top of the tee slot. Otherwise the nut will just lift up and again the clamping force will be lost.
Here is the little XY table I made tee nuts for:
Anyway, I suggest you make a drawing and double check your measurements. It's a lot less confusing if you have a drawing to work to.
I'm not going to go into a lot of detail on how to tram the vise on a shaper. Briefly, to set up the shaper, start by aligning the fixed jaw of the vise parallel to the ram axis. Use a large machinist square set against the vertical slideways to make sure that the vise is square. It's a real good idea to have gone through your vise with a dial indicator, shimming as necessary with cigarette papers. The fixed jaw should be vertical, and the bed of the vise should be horizontal. The accuracy of all your work depends on that.
Choose a length of steel long enough to make the desired number of tee nuts plus a generous cutting allowance. I generally make up tee nuts 4 at a time and make them about an inch long so I cut a length about 4-1/2". Pick a piece of stock that is larger in both dimensions than needed.
The first thing to do is to machine the part to the base width.
Install a basic cutting tool in the shaper. End rake, side rake, top rake, honed razor sharp. I don't have a good picture of the bit I used but this may give you a general idea:
Put the block in the vise, supported by parallels as needed. Take a roughing pass across the part just deep enough to get below the scale. Then reduce the feed and do a finishing pass. The next two pix show my piece of stock in the shaper vise before I make any cuts on it, and then after I machine the first surface:
Remove the part and deburr.
Put the part back in the vise with the machined side down on the parallels. Set the feed to the highest rate and take roughing cuts as deep as the machine and setup will tolerate until you are about 0.010" oversize, then switch to a fine feed and take a finishing cut to the final base width.
Remember, on tee nuts it's OK to be a few thousandths undersize, but if you leave the nuts oversize they either won't go in the slots or they will be difficult to use.
With the part being on parallels, I was able to use calipers to measure the dimension between the two machined surfaces:
Remove the part and deburr. The next step is to machine the block to the overall height of the tee nut (base height plus tongue height).
Put the part back in the vise, placing a machined side against the fixed jaw of the vise. Take a rough pass across the top just deep enough to get below the scale. Then reduce the feed and do a finishing pass. Remove, deburr and replace the part with the last unmachined side up. Take multiple roughing passes and one finishing pass to bring the part to the correct height.
Remove the part and deburr.
Here is my block machined to the correct width and height:
Apply layout ink to the top side and to the two sides from which the flanks will be machined. (This is one of the places where it's easy to get confused on which side is which. Don't be fooled here.) Lay out the tongue width down the center of the top, and the flank depth on the sides.
This time I chose to set an adjustable parallel to size and use it as a scribing block to make the top lines:
If you look carefully at the next picture you can see my layout lines:
Put the part back in the vise with its top side facing up. Make sure the part seats solidly on all 4 corners. Use cigarette paper shims if necessary to check. Also, make sure the part is mounted high enough in the vise so that you can see the layout lines on the sides.
It isn't easy to convey the shape of a cutting tool bit in a photo. Here is a picture of the side cutting bit I used:
Install a side cutting tool. This tool has to have a 90° angle ground into its tip, with the sides relieved and some back rake. Use a strong light and a precision square to set the bit exactly vertical/horizontal. The next image shows how I set the bit correctly:
Set the machine to a slow speed, as you will be feeding by hand. (It's tempting to use power feed for the horizontal advances, but it's very easy to mistime stopping the ram. Feeding by hand is slower but makes it much easier to get the cut right.) Set the machine to a medium depth of cut (on my 12" shaper I set it for 50 thou cut) and disengage the automatic cross feed. Put the crank on the cross feed shaft. Start the machine and advance the cross feed manually. Keep an eye on the top layout line. It's OK to let the machine take two or more strokes between manual feed advances, while you think about how much to feed. Sneak up on the layout line and stop ten or fifteen thou short. Crank the table back, increase the depth of cut and repeat cutting horizontally, stopping about where you stopped before, a bit short of the layout line. Continue down in this manner until you are close to the side layout line. Do not go all the way down. The goal here is to rough out the flank and to leave material for finishing passes in both directions.
I did take a picture after the first horizontal pass. If you squint a little you can see how the cut stopped short of the layout line.
I also stopped partway through roughing out the flank and took a photo. It may illustrate how you take multiple horizontal passes to rough out the flank material.
You have probably noticed the burrs left by the cutting tool in previous pictures. The next step is again to remove the part and deburr. Sometimes when the burr is exceptionally heavy it's convenient to use a small chisel and a hammer and tap your way along to remove the heavy burr. You can see how this went in the next photo:
Clean the parallels and the vise. Now install the part the other way around. Again, make sure the part is fully seated on the parallels just like before. Rough out the other flank. Repeat what you did on the other side, feeding by hand and shopping short of the top and side layout lines. As you finish, after the last roughing horizontal pass, brush off all chips and use the caliper depth rod to measure from the bottom of the flank down to the parallel the part is sitting on. This measurement is the base height. Here is how I measured:
Subtract the target base height from your measurement and advance the vertical slide exactly that amount. Then take a horizontal finishing pass, stopping just short of the tongue edge like before. Stop the machine. Do not adjust the depth of cut. Again use a caliper depth rod to check the base height. If necessary, take one more small horizontal finishing pass. Once you have hit the dimension do not touch the vertical slide. Remove and reverse the part, cleaning the vise and parallels and ensuring the part is fully seated on the parallels, then do the horizontal finishing pass on the other side without moving the height of the toolbit. This way both sides will be cut to just the same height.
Raise the cutting tool. Position it above the tongue edge, on the top layout line. Now you will need to do some simple shop math. Subtract the design tongue width from the design base width and divide the result by 2 to get the flank width. Add that number to the width of the tongue. Write down the result. This is the correct tool offset from the rear edge of the part.
Feel the part just above the movable jaw. If there is a burr (there shouldn't be) remove it with a small file without removing the part from the vise. Put a small precision square on the movable jaw against the edge of the part so its blade stands straight up. Use the inside measuring capability of the calipers to set the cutting tool the correct offset (which you just calculated) from the part edge (the vertical blade of the square). Here's a picture of that measuring setup:
Remove the square. Start the machine and advance the vertical slide by hand to feed the machine down the flank. Again, it's OK to let the machine take two or more strokes without advancing the depth, to let you collect yourself. Sneak up on the flat, taking very small cuts at the end until the vertical face just meets the horizontal cut, leaving a clean corner. You may need to remove chips and use a strong light and possibly magnification to see if the corner is fully machined. When the vertical finishing pass is complete, stop the machine. Retract the vertical slide without touching the cross slide. Remove, deburr and reverse the part, and repeat the vertical finishing pass for the second side to complete machining both flanks. Because you didn't move the table horizontally, both flanks will be the same depth and the tongue will be right in the center of your part.
One last time, remove the part and deburr. At this point on some tee slot topologies you can slide the whole part in to make sure it fits. Mine did, although it binds up on some globby paint inside the tee slots:
Now you are done with the shaper portion of this task. The rest of the job doesn't involve the shaper. Lay out, drill and tap the holes. Take your time drilling the holes - it's important that the hole be right in the middle of the tee nut. Also take extra care to start the tap truly vertical. Saw the part into individual nuts. Debur the finished nuts carefully. Stake the threads on the bottom with a small chisel to prevent bolts from extending through. If desired, clean the parts and blacken them.
That's it! I suggest now that you've done one set, that you make drawings for all the other tee nuts you need in your shop and make them too while this process is fresh in your mind.
Thanks for reading!