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Member postings for John Purdy

Here is a list of all the postings John Purdy has made in our forums. Click on a thread name to jump to the thread.

Thread: Sanderson Beam
14/05/2022 02:17:45

Finally finished the con rod, pump rod and the strap links connecting the piston rod to the beam. So it's time to stop procrastinating and tackle the parallel motion links.


The plans show the links with 7/32" dia. spherical ends thinned down to 1/8" thick and the body fish bellied 5/32" in the middle and 3/32" at each end with a short parallel section 1/8" dia before the spherical end. Question is how to make then. If the centre section is turned first then how to hold it to turn the ends seeing as how the there is nothing parallel to hold. If the ends are turned first then how to hold it to turn the fish bellied centre section?

After considerable head scratching I came up with this idea. Starting with 1/4" dia. rod, drill and ream the two 1/8" end holes using coordinates in the mill, spaced .109" in from each end. Use a form tool to turn the spherical ends and the short 1/8" parallel section. Now the centre section can be turned by holding the left hand end in a specially made jig on the end of a piece of 1/2" square material held in the 4 jaw with the right hand end supported in a small female live centre in the tail stock.

The form tool to turn the spherical ends of the links was made from a piece of 1/2" W1 drill rod. Held in a 5C collet in a collet block and set at a 3 deg. angle in the vice the end was milled down to half dia. This gives some back rake to the cutting edge. The collet block was then re-positioned at a 7 deg. angle to give the front clearance and a 7/32" end mill was used to angle the front edge and then, on the centre line, plunge down for a further .109" to form the half circle cutting edge for the ball. The ear, on what would be the chuck side when used, was milled back to leave it .047" from the centre of the 7/32" dia. ball to form the 1/8" dia. collar.


The jig to hold the end of the link in the 4 jaw was made from a piece of 1/2" square steel from the scrap box with the end milled down to 1/4" for 11/16". Dimples were made in it and the cover, 1/8" in from the end, with a 1/4" 90 deg. spotting drill followed by a #3 (1/4" ) centre drill. The depth was adjusted so the link longitudinal centre line was on the centre line of the 1/2" bar. An 1/8" end mill was used to cut a slot .060" deep on the centre line into the dimples to provide clearance for the 1/8"dia. collar on the link. The central hole was drilled through and reamed 1/8". The two pieces were clamped together with an 1/8" rod through the central holes for alignment and drilled and tapped for an 8-32 screw to clamp them together. The pin is an easy fit in the 1/8" holes in the jig and link to provide some clearance for alignment and to provide a positive drive. It is retained from falling (flying ) out by thin sheet strips riveted to outsides of the two pieces.


One eye turned on the end of an embryo link with the form tool.


Using a dial indicator on the 1/8" dia. collar to centre the link held in the jig in the 4 jaw. The other end supported by a small female live centre in the tail stock. The female live centre held in the drill chuck is a Unimat live centre modified by disassembling and pressing the male centre out of the bearing and pressing in a home made small female centre .


The centre fish belly roughing out finished. Just needs some work with a fine file to blend the flats together and polishing with some fine abrasive cloth.


The jig set up in the mill for machining the eyes down to 1/8" thick. The jig isn't my idea, it's from Tubal Cain's write up in ME of the "Mary" beam engine. The clamp is my addition and is done up just finger tight to prevent the possibly of the link moving up under the milling forces.


A finished link. Only 7 more to go!



Edited By John Purdy on 14/05/2022 02:22:13

Edited By John Purdy on 14/05/2022 02:29:34

Thread: Locomotive threading
05/05/2022 17:38:06


Here's the conversion chart I have developed to convert BA to UNC/UNF threads which I have used on my projects. I normally make all my hex headed screws and nuts from hex stock. If you want I can email you a PDF of the chart if you PM me your e-mail address.


dscn2959 (2).jpg

Edited By John Purdy on 05/05/2022 17:41:39

Edited By John Purdy on 05/05/2022 17:54:06

25/04/2022 20:09:30

Still haven't received MEW #313 or ME #4685 25 Feb. Have received #314, #4686 and #4687 (4687 last Friday ). Any other subscribers in Canada missing those issues or is it just me? Not surprisingly inquiries to MTM have gone unanswered.


Thread: Sanderson Beam
12/04/2022 02:28:17


On Clarkson's model of the Sanderson beam engine the straps, gibs and cotters on both the big and little ends of the con rod are only simulated. The ends of the rod being a closed slot to simulate the strap and the split bearings held in by single tapered cotters. Not sure why he designed it that way as the bearings on the pump rod and the connecting links between piston rod crosshead and beam use proper straps, gibs and cotters.


12/04/2022 02:16:30

    Thanks for the pertinent section of the current plans. It looks like the basic dimensions of the slot are the same as my plans but a lot of other dimensions are given which makes it much clearer. Currently the slot in my rod is 5/16" wide for the whole length so I will have to mill/file out the bottom 3/16" to 7/16" wide. This will allow the 5/32" deep bottom half of the bearing to be inserted and slid up to mate with the top half.
    I also see there is a note at the bottom left of the your image that says to remove the inner flange on the top half of the bearings. I would think that it could be put in at 90 degrees and then rotated and slid into position, so is there a reason given for why the flange is to be removed?
    Did a trial assembly of the beam, pump rod and pump body and found that with the rod made to 6" between bearing centre and pin at the bottom as per the drawing, it is just too long, with the end of the rod hitting the top of the pump body. So back to the torch to un-solder the end, cut 3/16" off the rod and re-solder it back on. Fits much better now as can be seen it the picture.

pump rod 2.jpg

Edited By John Purdy on 12/04/2022 02:17:59

Edited By John Purdy on 12/04/2022 02:31:21

11/04/2022 17:55:59


Yes, that is the only drawing of the con rod little end and its bearings that is on the plans. Sounds like these dimensions have been changed. It would be interesting to see how these are shown on the current plans.

As for the pump rod bearings the plans show the beam pin journals as 5/32" dia. but the bore of the split bearing as 3/16" dia. which obviously doesn't work. I opted to make the bore 5/32" to match the beam pin journals for the reason given above.


10/04/2022 20:31:15

Thanks for your reply.

I have finished the pump rod but made the bearing bores 5/32" to be the same as the pin as drawn. Seemed like a better idea than a 3/16" bore as shown, as that would leave only a 1/32" wall in the bearing. (Note he cotters are still over length and will be shortened on final assembly when the bearings are run in. )

pump rod.jpg

Below is a snippet of the drawing of the little end of the con rod (not too clear as I said the drawing is well faded ). The drawing appears to show the slot as being stepped, 5/16" wide where the bearing is and 7/16" wide down to the bottom of the slot. As shown the bearing is 7/16" across the flanges but the depth of the square bottom half of the bearing is greater than the length of the 7/16" width of the slot, so how is it to fit in? How does this drawing compare with your newer one?

little end.jpg


09/04/2022 18:34:00

Don and Neil

I am also missing MEW 313 here in Comox BC. Got 314 two weeks ago and 312 about 2 months ago. Naturally the missing one is the one with my article in it!


Thread: Pipe lagging
05/04/2022 17:31:38


I have used thick bucher's cord (cotton string about .070" in dia. ) wrapped around the pipe, ends held in place with a drop of CA glue, and painted with flat white acrylic paint. Looks quite prototypical. You can see it on my Clarkson's compound mill engine picture.


Thread: Detroit Hydrostatic Lubricator
30/03/2022 22:21:20


I've just re-sent my PM.


30/03/2022 21:42:46


I just checked my sent box and it shows my message as being unread. Have you checked your message inbox? Its the envelope shaped icon in the login line at the top of this page, between "Settings" and "Friends". It should be flashing.


28/03/2022 17:47:45


I've sent you a PM.


Thread: Sanderson Beam
20/03/2022 17:40:04

Having finished the Stuart beam engine I've decided its time to finish the Sanderson beam engine. Its only been 42 years since I started it! Starting with the con rod I find that the casting is slightly over 1/8" too short to make to the drawing dimensions. After some head scratching and many calculations I have come come up with a length between bearings that I think will work and just fit within the as cast length. Now the next problem is, there appears to be a number of errors/discrepancies on the plans for the little end of the con rod. The plans show the bearings as being 5/16" wide but the journal in the beam pin for the bearings only 1/4" wide. If the bearings were 1/4" wide with the arms on the fork 3/16" wide (vice 1/4" wide as shown ) which is how the drawing scales (not always a safe idea! ) then it would fit. Also, as drawn, the bearings appear to be impossible to fit into to slots in the fork end. The slot is 5/16" wide but the bearing halves have a 7/16" wide flange on each side. The top semi-circular half can be put in sideways and rotated into position, but the square bottom half can't be fitted. I have a couple of ideas for a solution, but what have others done?
Another discrepancy is the bore on the pump rod bearings is shown as 3/16", but the pin journals are 5/32" dia.
The plans I have are original Clarkson's dye-line, dated 18/10/69 and are well faded, having been exposed to sunlight for too long.
I'd be curious to know if these errors show up on the current plans.


Thread: Myford Super 7 gib screws
16/03/2022 18:52:49

I should have said my lathe is a S7B with power cross feed. As Speelwerk says the saddle and the apron are different from the earlier non power cross feed model, thus the screws will be different.


16/03/2022 16:53:18


On my S7, serial # SK127323 mfg 1976, the screws are all 1/4 BSF threaded full length, screwdriver slotted end. Lengths as follows left to right: 2.750 round point, 2 910 dog point, and 2.750 round point. The holes in the saddle are counter bored .275 dia. by 1.950 deep.  Hope this helps.


Edited By John Purdy on 16/03/2022 17:09:42

Thread: ML7 oiling advice
03/03/2022 17:48:23


This is what I use on the oil nipples on my Myford. Its on the spout of a standard pump oil can. The end is turned down to just fit in the hole in the nipple and a small slot is filed across the end. In use it is pushed down into the hole in the nipple sealing on the curved surface, the end depresses the ball and the slot allows the oil to flow into the nipple. Works very well and costs nothing ( save the oil can ).



Thread: M&W Micrometer Lock
28/02/2022 20:25:00

I just received the locking ring from Paul. For anyone needing to make one I have measured it under high magnification (20X )and the thread is 55 deg., 50TPI, .388" OD. The bore tapers from .273 on the outside to .325 on the inside and the rest of the dimensions are as Paul has shown in his post I measured the angle by comparing it with my small 60 and 55 deg. threading tools which were ground on the Quorn so should be reasonably accurate.


Edited By John Purdy on 28/02/2022 20:26:42

Thread: Hand Hacksaw
26/02/2022 19:07:55

I have a Starrett as in the picture, and it works very well. The blade is tensioned by turning the lever at the top right. As far as I know it is still available as it is still listed by the tool suppliers I use.



Thread: Reverse Lever
22/02/2022 21:13:39

Is there a convention on engines with reverse controlled by a lever, such as the ST5A etc., for which is forward, up or down? When I try to think about it logically I can make a case for either.


Thread: Stuart #1 Reverse Drawings
20/02/2022 20:50:31


I've sent you a PM.


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