Construction Notes For profile copier

Construction Notes For Profile Copier

Download Drawing .... not ready yet, by 7/11/96 approx.

This modification of the taper turning attachment facilitates the copying of turned work, and also the generation of 3D shapes from 2D formers. An item such as (for example) a ball handle is mounted between the centring heads and a pointer connected to the cross-slide follows the contours. A blank mounted in the lathe chuck is thus machined to the same shape. As the profile copier only uses two dimensions whilst following the original, simple shapes can be used to produce 3D turnings. To produce a ball, dome or bell shape (for GWR fans!) only requires that a cross section be mounted, or more correctly a half cross section. In the first case the ball could be generated using a simple parted-off slice of round barstock, in the second a vertical mid-section shape could be cut out and filed up from brass sheet.

What the attachment won't do: remember that the stylus or pointer has a finite width, therefore it is unable to follow 90 degree corners (at least, not on both sides at one setting). In the worst case, if copying a complete 1" sphere with a 1/16" wide 'V'-pointed stylus the copy would end up 1-1/16" wide (not 1"), 1/32" being added to each end. The extra width would commence at the point where the tangent with the tip 'V' angle meets the curvature of the sphere. For the purposes of making a ball-handle this would require a little correction with a file on the very end to restore appearances. With a dome, the stylus can be set-over to point to the left, and the problem would not occur, in fact it could also be minimised on the ball handle by doing the same considering that a complete sphere is not cut - the connecting shank representing some 20% of the diameter. In any case, you cannot cut a complete sphere as it would not be possible to mount the former such that the stylus could trace the entire outline.

To make this device you will need to have previously made the taper turning attachment, or perhaps already own the Myford equivalent (or any other make of course) and are prepared to modify the design to suit.

Centring Heads

These are made from a length of 2" square bms about 5-1/4" long. This will be sufficient to make the two heads allowing for cutting. Each head is 2-1/2" high with a dovetail on the bottom to suit the slide arm, and a horizontal bore to locate the centres. Cut the bar in half and face one end of each block square in the 4-jaw or on the milling machine. First job is to machine the dovetail slot, and this is best done as a pair so that the blocks align on the slide arm. Mount the two blocks with their un-machined ends upwards in the milling machine vice and use a fly-cutter to face them to the same length - it's not essential that the 2-1/2" dimension be exact. If done in the lathe this job will require a bit of wangling, and it's probably best to clamp them down on to an angle plate attached to the vertical slide. Mark a centre line across both blocks together, another line 0.334" above it and a third 0.459" below it. Mill a channel between the two lines 0.325" deep using a 1/2" slot drill, and check the exact width with your calipers rather than relying on machining to the line itself. Use your dovetail cutter to form the 30 degree angle leaving a witness of about 10-20 thou on the sharp corner. The last cut should shave both side and bottom of the channel, aim to get a good finish here.

When I made the prototype I bored the holes for the centres next. In view of the problems I had aligning the blocks for machining it would probably have been better to complete the dovetail mounting by making the gib strip and fitting the adjusting screws. So, mark out the positions of the five screw holes on each block and drill them 4BA tapping size (No.31). Use a length of 3/32" x 1/2" ms flat to make the gib strips, machine one edge to 30 degrees and fit it into the block's dovetail and mark the required width, then machine the other edge to 30 degrees also. The edge of the gib strip should be a few thou below of the sliding face, and the same length as the block (2"). Assemble the block and gib strip onto the slide arm and use a tool-maker's clamp to hold it in place. Poke the No.31 drill down the holes and make indents on the gib strip. Finally, tap the holes in the block 4BA. With this part of the job complete you are now able to mount both blocks onto the slide arm and hold them firmly in place by tightening the gib strip adjusting screws.

Boring the centring heads using the lathe.

You will want to bore the holes for the centres next. As with the dovetail slots, it's best to tackle this job with the blocks mounted as a pair so the bores are exactly aligned. You can use the slide arm to mount the blocks, on the Myford S7 with the slide arm resting on the boring table, the blocks will be at the correct height for boring. It's important that you use the slide arm dovetail to set it parallel with the lathe axis, this is the datum surface. I made a mistake here by using the bottom edge of slide arm which was a few thou out of alignment with the dovetail. This resulted in the bores for the centres being cut at an angle, and having discovered this later I had to bore again oversize and press in a sleave to correct the situation. In fact, this error would not have been too much of a problem for the profile copier, but I intend to use these centers for something else and I wanted them to be accurate.

The completed centring heads mounted on the dovetail slide arm.

Mark a centre line on the block face nearest the headstock and align the lathe centre with this. You want a hole 3/4" diameter through both blocks, and the procedure I used was to centre, drill 1/4" followed by 1/2" and 23/32", then bore out using a small boring head to 10 thou under 3/4" and finished the bore with a machine reamer. I realise many folk will not have either boring head nor 3/4" machine reamer, and this being the case there are a number of other options. You could manage with smaller centres (say, 1/2"), I had reason to use 3/4" because I also used the same bore to mount a drill chuck having a 3/4" plain shank. You could also use the 4-jaw as an improvised boring head, the cutter being offset by making it run eccentric - you will probably not get exactly 3/4" this way though, so you would have to machine the centre to fit the bore. It's unfortunately difficult to use a between-centres boring bar because the length of the slide arm extending out the back of the boring table means the tailstock cannot get close enough to support it (unless it's an extraordinarily long boring bar!).

I made my centres from 2-1/4" lengths of 3/4" silver steel, set to run true in the 4-jaw and machined to a 60 degree included angle before finally hardening and tempering to light straw. Next job is to machine the bore end caps. These are a press fit (plus Loctite #601 to make certain it doesn't move) in the end of the bore, one is required at opposite ends of the two centring heads. They have a central threaded hole 5/16" x 32 tpi to accept the adjusting screw, which is made from 3/4" brass rod with the head knurled. A clamp screw (1/4" x 26 tpi) is placed at the side of the block to hold the centre in position, the screw again made from brass with a knurled head. Finally, the dovetail clamp screw to fit the centre of the 5 holes in the base of the heads (the other 4 occupied by the adjustment screws) is turned from 5/16" brass rod.

Holders for sheet metal formers. Be very careful trimming the ends otherwise you may end up with something that looks like the one on the far left!!

Sheet former mounting heads.

I originally conceived a very simple mounting for the sheet formers, but a bit of thought made me realise something more accurate was called for. Start with a 2-1/2" length of 3/4" silver steel, face both ends then center and drill right through 1/4". This will test your lathe because you want this hole central. Follow this with a 31/64" drill right through, and if you are in any doubt about the concentricity skim the hole with a boring tool. Then drill (or bore) 5/8" diameter to a depth of 1" before reaming through the remainder 1/2". Next job is to set vertically in the milling vice and use a 1/16" slitting saw to saw to cut half-way through at a point 1" from the end (at the end of the 5/8" bore), then make a single longitudinal slit along the 1" length to meet the first slit. Use Loctite #601 to cement a 2-1/2" length of 1/2" diameter sliver steel into the reamed hole. This will leave an annulus 1/16" wide, and a compressible 'flap' at the top which will trap a piece of 1/16" sheet metal like the jaws of a vice, two screws being used to close it. The 1/2" diameter center piece will act as a datum edge which the sheet former can be pressed against so that it is parallel and square to the axis of the centring heads. (You'll get a clearer idea looking at the photo and drawings). With the lateral slit uppermost, mark off the centers for the two 2 BA cap head screws, then drill No.22 and tap 2 BA, then open out the holes in the top 'flap' with a No.13 drill. It would be nice to use 2 shaped washers under the screw heads to save marring the surface but this isn't critical. Don't over-tighten the screws or you might damage the fitting, there is really no need to as it has adequate clamping power and the stylus cannot push the former into the fitting because of the solid center piece.

Stylus

Stylus mounting bracket.

The stylus (or more correctly, the styli) will need to be interchangeable, so a new mounting bracket will be required. You will be able to copy the outline of the end plate already made if you have built the taper turning attachment, otherwise follow the drawings. The cut-out for the dovetail is not required for this endplate, the cross-slide will not be required to be withdrawn far enough for this to pose a problem. A piece of 3/4" square bms 2" long is screwed to the back plate with 4 BA countersunk screws, this bracket has a 3/8" horizontal slot in the end 0.520" deep to accommodate the styli which are held in place with a single 6 mm cap-head screw. The bracket is slit with a fine slitting saw to allow it to compress thus gripping the stylus. The styli are either made from the solid (3/8" square material) a 6 mm hole being provided at one end to fit the bracket and the other end cut to shape, or alternatively they can be fabricated from a 3/8" long piece of round mild steel, drilled 6 mm, and the blade subsequently silver soldered on. The styli will vary in length (reach) and tip design dependent upon the job required, a couple of examples are shown. It might be better to case-harden the styli or make them from 3/8" square silver steel to prevent them being damaged by knocks, but it probably isn't essential.

Using the Attachment

I expected to use different stylus shapes for different jobs, and so the mounting allows them to be interchanged. It's preferable to use the most rigid stylus possible and this of course is opposite to the requirements for following intricate shapes where the finest stylus possible is required. Thus the shape/length/width of the tip is a compromise taking into account the job in hand. In most cases, the lathe tool doing the cutting would preferably be of the same shape and dimensions as the stylus. For example, if the stylus tip radius is 1/32" and 1/2" long then for best results the lathe tool needs to be ground to a similar shape.

Overhead schematic of the use of a 3D model.

To continue with the example of the typical small ball handle (3/4" and 5/8" balls). A 3D model, if it were available, would be lightly centered at each end and mounted between the centring heads. The stylus would have a 1/16" blade some 3/4" long ground to a 'V' with a slight radius, it would be mounted pointing 2-3 degrees to the left and the 6 mm screw tightened. The lathe tool would have a similar profile (perhaps with more of a radius). A blank of 3/4" diameter would be set up in the lathe and rough turned to the approximate shape. The stylus would be moved so that it is touching the major diameter of the larger ball (on the right), and the lathe tool moved using the top-slide (set at about 30 degree angle) to just touch the diameter of the blank where the center of the ball will be. Left-right adjustment can be made by moving the blank in/out of the chuck, moving the centring heads along the slide arm, or using the center feed screws. With the datum point set the blank can be roughed out by use of the combination of traversing handwheel and cross-slide feed, cuts being made as if using a parting tool - moving inwards until the stylus touches the former. Finishing is achieved by releasing the cross-slide screw and using the hand to press the cross-slide (and stylus) against the former whilst again using the handwheel traverse. The cross-slide must be correctly adjusted for this to work well (i.e., free to move without binding). I have found the best way is to set the toolpoint at the maximum diameter of the ball (or whatever), and pressing firmly inwards with the left hand turn the traversing handwheel.

If a 3D model were not available it would not take much effort to mark 2 semi-circles and a tapered line for the shank, cut out from 1/16" brass sheet leaving sufficient to grip in the sheet metal holders, and use this as a guide for the lathe tool. The diagram below shows the setup for this job from above.

Overhead schematic of the use of a sheet metal former.

Using a former to make a ball handle. Ball handle roughed out to shape using straight inward feeds.

Finished ball handle. Shank ended up too narrow (marked out in a bit of a hurry!) but the balls are well formed.

Stages in making a bell

Below is a pictorial sequence of the stages in making a small (1-1/2" dia) brass bell. The former literally took 5 minutes to shape up using a linisher and a fine needle file. The turning took little longer. Cleaning up the brass swarf took *much* longer!! You can keep a stock of these simple formers for future reference in case you need to make an identical part, they take up little space.

Note that the bell is solid at this stage, to make it hollow I would proceed as follows:

Before parting the bell off from the parent material solder on a chucking stub (1/2" dia would be fine) and turn it so that it runs truly with the bell body.
Part off and turn around in the chuck, holding the bell by the chucking stub. Remove the former from it's holders and turn it around 180 degrees.
Rough out the interior of the bell with drills and a substantial boring tool to reduce the burden on the finishing boring tool.
Position the stylus such that it is touching the former at the outer corner of the bell shape. Position the boring tool point (with top-slide) such that the desired wall thickness will remain at *both sides and end* when the shape is traced. (in other words, if the wall thickness were to be 1/8" the tool point would be 1/8" to the right and 1/8" inwards).
Simply follow the contour of the former as when turning the outside.

I guess this might seem like a long-winded method, but what you are doing is a complex job and probably cannot be accomplished any other way. To get a bell shape with a substantial wall thickness usually involves casting and then still requires finish turning (spinning will work with thin material). You can of course use a casting as your starting point and use the profiling attachment to finish turn it. Larger bells would involve an enormous waste of metal if turned from the solid - and with my experience of the small bell I sure as h*ll wouldn't want to clean up afterwards...

- Basic shape roughed out. Note that the cross-slide feed screw is still connected at this stage.

- Shape is finished turned, feed screw has been disconnected for this job.

- Finished bell, and the simple former used to make it.

Other uses

Another use for the device is to copy multiple tapers, such as the twin tapers of a Morse taper Jacobs shank. The center heads need to have been accurately made for this class of work to be successful. Below is shown the setup for machining a 1MT drill chuck shank. To set the centring heads in the first instance requires the use of a centered parallel bar (easily made yourself) and a DTI, the twin centers being set parallel with the lathe axis. Using the index zero mark alone is probably not accurate enough, but I haven't tested this theory - it's just an assumption. Once this setting has been accurately achieved a 5/32" hole can be drilled and reamed through the swing arm and base for a dowel pin (just as you did for the 2MT reference point for turning a standard taper) so the position can be accurately reset without further reference to the DTI.

Setup for copying a 1MT Jacobs taper shank.

Yet another use is to produce items such as the crowned pulleys wheels for a linisher (belt sander), these being curved they cannot easily be made any other way (filing them to shape is a real pain). With the attachment all you would need do is mark off an arc on a piece of brass sheet to make a guide piece, file to outline and mount the guide on the slide arm. The stylus will faithfully trace the shape and a perfect crowned wheel will result.

How about uses other than model engineering, you can make nice wooden door knobs from a pattern - any fool can make one fancy shaped door knob, not so easy to make a dozen all exactly the same. What about matching candlesticks, and any number of other decorative turned items that need to be the same shape.

Back to previous page