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Member postings for Robert Dodds

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

Thread: That Strange Calculator Again
15/01/2022 17:59:51

Next stop should be The Arithmeum,. Bonn University. It has a museum of mechanical calculators, lots of them are circular and there are 10000 exhibits to check out. Some of the detail is in German so you may need some translation before calculation.

https://www.arithmeum.uni-bonn.de/en/arithmeum.html,

Bob D

15/01/2022 17:48:39

Worth a click on this site to see it in operation.

Note the right thumb on the black bar to stop the inner ring rotating until required

https://imgur.com/a/Nfe12p0

Bob D

15/01/2022 15:53:44

I've just looked back at Grindstone Cowboys earlier link to reddit. Trawling down to KarenEiffel's response led me to an illustrated book of Rechnenmaschinen. Look a bit familiar?

reddit.jpg

addall.jpg

summus.jpg

Bob D

14/01/2022 22:39:40

I'm a long way from understanding this device but I do wonder whether it might have had some pins or similar that went into the small holes of the inner disc and circle and registered them in set positions for some setting purpose.
I'm intrigued by the number sets that are evident on the device, 12,16,20,48. all of which had monetary associations back in the day and additionally were associated with the avoirdupois weight system, ozs, lbs cwts. tons.
I recall the time when banks had scales to weigh your little blue bag of copper or silver coins and that one old penny weighed a third of an ounce so 48 weighed a pound and a pounds worth of pennies weighed five pound!
I am further intrigued by the fractions in the outer segments particularly the ones with an addition appended.
If you change the + sign to - and count the addendum as 1/48th ( 0.020833) in every case the resulting sum then equals the simple fractions in the same segment.

Segment 6 3/8 2/5 -6(0.020833) = 0.375

5/12 -2(0.020833) = 0.375

Has this got any significance?

Bob D

Thread: Half nut skipping still
28/11/2021 15:58:17

Steve,

Will your 6mm rod pass through the vertical slots in the apron or are they designed for 3/16" rod.in which case you will need to make them look like cheese head screws.

Reference the symmetry I wrote about, check the two dimensions indicated on your edited photo and see if they are near equal. They will determine which of your half nuts moves most when you rotate the "banjo"

measure.jpg

Bob D

28/11/2021 13:05:04

Steve,

In making those 6mm pins do make sure that the 3/16" thread is concentric as possible with the 6mm O/D.
If you are struggling with that please PM with your dimensions and I'll help out.

As a last resort to avoid shims on the Apron the 6mm pins could intentionally be made eccentric to the threaded portion and thereby vary the engagement position of the half nuts, but that's not for the faint hearted.

27/11/2021 21:51:55

OK Steve,


My pins measure 0.250" -.001 and the slots take a letter E drill shank (0.250" end to end whilst a letter F drill (0.254"is tight in spots. With the lever assembly off it's pivot pin the two pegs slide freely up and down as long as I align the nuts and leadscrew. Move the saddle a 1/16", lifting the top nut up out of mesh while the.bottom one falls out of mesh under it's own weight and the two half nuts are restricted in movement until I move further and realign with the leadscrew.
I've never had occasion to remove the apron but I cannot detect any shims or need for any. Remember, adding excessive shims also affects the engagement of the rack and pinion associated with the manual feeding of the saddle. With the half nut mechanism reassembled and the threads aligned to the leadscrew I can engage and disengage the half nuts and detect no movement or strain on the leadscrew anywhere along the length of the saddle movement.
The earlier thread of yours about wonky threads on the pins that screw into the half nuts may have some bearing on the problem . There has to be some symmetry about those pins, the half nuts and the leadscrew. A wonky screw will cause one half nut to engage before the other and that, together with excessive clearances to the two slots and you will get the sort of disengagement problems you are seeing.

Get your slots uniform in size and round particularly at the nut closed position. then produce two pins of a diameter to suit your slot size less 0.002" to 0.005"and get the thread as concentric as possible . I would remove shims at initial tryout as I doubt that it left the factory with shims. After all they cost less than £20 in the thirties so didn't get much individual attention.
Clear out any burrs or dross that may still be in the dodgy half nut and whilst loose, check it's engagement with the leadscrew. Put it all back together and with the nuts/ leadscrew aligned check to see if the leadscrew is being lifted/ lowered as you engage the nuts.
Once again I would say, not as a recommendation but as matter of fact, your machine should be able to screwcut with one half nut just a plain bore to suit the O/D of the leadsrew. The other half would do all the work and feed the saddle along. After all your quick release engineers vise only has a half nut and see what forces that can stand!!

img_20211127_182441.jpg

Regards Bob D

Edited By Robert Dodds on 27/11/2021 21:56:25

27/11/2021 15:49:44

Steve,

I've just had a closer look at my Zyto and taken a couple of shots of it.

When i look at your first photo there appears to be a substantial clearance between the scroll slots and your pins,( wobbly threads on another query) On my machine the pins are a reasonably close fit to the slots and my take is that your slots are badly worn or maybe modified. It is the proper fit of these pins in the slots that gives you the lock in of the half nuts. You need a, uniform width slots and b, good fitting pins in the whole length of the slots to keep the half nuts engaged.

img_20211127_143032.jpg

Not to be recommended but strictly speaking a single thread on your top half nut should be sufficient to produce a good screw thread on your workpiece, at least for a limited time!

I notice that you do not show a large washer over the lever assembly. For what its worth mine has a full diameter cover washer which has a tapped hole in the centre. The pivot shaft has a screwed extension onto which the washer screws and then it is locked in position with a domed nut, which is then used to control the fit of the lever assembly . Too tight and you can't turn the lever.

img_20211127_143240.jpg

Depending on your skill level I would be filing out the slots to a suitable drill shank al the way along the slots, then making two oversize pins to suit the slots and having another go.

Regards Bob D

Edited By Robert Dodds on 27/11/2021 15:52:44

Thread: Axminster Drill Clamp
21/11/2021 20:15:38

Very useful but do fit a heavy gauge flat washer next to the eye-nut under the table. Depending on the rib configuration on the underside of the table a hex nut may be more versatile than the eye-nut.

Bob D

Thread: Peter Gilliland
02/11/2021 18:44:41

Once upon a time there was trader selling Atlas spares. I got a pair of half nuts and some change gears from him I recall but I can't remember any contact details. Anybody had contact with him in the recent past?

Bob D.

Thread: What is it
30/10/2021 21:27:27

A hint about the size might help. I have some reservations about valve guide de-coking, it's mainly the stem immediately under the valve head that gathers coke.
Depending on size, is it possible it would be used for cleaning out a gun / rifle barrel.

Bob D

Thread: Strange WW1 Chuck - 1MT
23/10/2021 22:05:26

Hi ,

I've dug out a similar design of chuck.
It is different in so far as the jaws are recessed behind a front plate that's secured by a couple of screws, Without destroying all it's patina there is no evidence of any makers mark just a 3/4" stamped on the periphery.
As with others it has 120 degree jaws which I had taken to imply that it was intended to grip hexagon bar etc. especially as the back end is screwed and counterbored to fit my Zyto, but that could be a later modification..
The overall quality of the parts appears to be very good and the complexity of the jaw design and their manufacture is impressive especially if it is, as earlier posters suggest, of 18th century build.

img_20211023_171950.jpg

img_20211023_172031.jpg

img_20211023_172135.jpg

Thread: Ideas on how to make up a G-Clamp Swivel Foot
18/09/2021 12:36:18

Hi,

I cheated.
I used some nylon bar, drilled out 8 thou less than the ball diameter and then used a round nose boring tool to make a snug fit for the ball end. Conventional shape for the rest of it and then part off. It has the added advantage of not marking the job.

Regards Bob D

Thread: Twinner Multi-Jigset (what is this tool for?)
25/08/2021 13:58:34

From the E bay photos they look like early forerunners of today's toggle clamps.
Graces Guide throws up some pictures of big positioners and welding fixtures for the welding trade made by Donald Ross and Partners under the name Twinner. from the phone number I guess the company dates from the 50's 60's era

Bob D

im195012wing-ross.jpg

im1955v200-p856bbb.jpg

Thread: Silver solder? ....... or what?
26/06/2021 22:15:30

My guess is one of the several varieties of SIF bronze. Father in Law used to use it for repairing cracked Cast Iron with an oxy-acetylene torch . It's Silicon Bronze with a dash of of silver and tin in it There are lots of suppliers still around, . give one a call to check the colour coding.

Regards Bob D

Thread: Pulley size help required.
18/06/2021 12:21:36

Old mart,

Your photos show your Atlas to be a later model than mine and I'm glad you can see a solution.
A note of caution regarding your speed range with the 3" pulley on the lower speed pair. You will then have raised your lowest spindle speed by 50% (3" instead of 2" > This may suit your purposes Ok but it depends on what your motor speed is and the type of work you will be doing as to what part of the overall speed range you will use.
I used an online belt length calculator ( https://www.omnicalculator.com/physics/belt-length ) and from it, assuming my scaling estimate of 8" for your centre distance in the photo is right and presuming a motor speed of 1400rpm your 2 choices of layshaft speed would be 466 or 985 rpm.
If you opted to keep the 2" pulley and fitted an inch shorter belt ((35" instead of 36" as indicated for 8" centres) and then made a 4.4" dia. pulley as the larger drive pulley you could expect a slower and wider ranging layshaft speed of 311 or 823 rpm.
As I noted before the choice depends very much on what your expected work range is.

Regards Bob D

Edited By Robert Dodds on 18/06/2021 12:24:06

Edited By Robert Dodds on 18/06/2021 12:49:20

Edited By Robert Dodds on 18/06/2021 12:50:33

16/06/2021 20:39:11

Question.

In my photo is the belt set to high or low speed ? With the second cone set to top speed it does about 600rpm with a 1400 rpm motor.

Bob D

16/06/2021 20:04:43

Old Mart,

I've got an Atlas with 2 speed primary drive. picture attached. Daft question but "do you have the motor pulley as my configuration? small motor pulley to large driven pulley, If not, try reversing the motor pulley on its shaft to look more like mine That works fine for me.

Hope this helps

Bob D

  1. atlas pulleys.jpgrt,

Thread: A bit more upcycling.
12/06/2021 21:33:34

Like it, A lot.

Bob D

Thread: Does anyone know what this is for?
09/05/2021 21:07:28

I think I can see two rollers, one at the handle side and another at the opposite side. Both have semi circular profiles and in one picture there may be a third roller which looks to be horizontally mounted in the same plane as the other two. I ask if this could indicate some form of wire bead folder similar to that which was used in auto construction in the 1930s.
Looking at images of bead forming machines highlights functional similarities between our mystery tool and some of the more recent designs of bead roller.

One maker has a video of making a bead rolled edge on a vintage Ford body panel that's well worth watching.
https://www.youtube.com/watch?v=eOcZwr-1Y1E

I can't explain the purpose of the outboard rollers but I think the primary tooling is hiding inside the head somewhere and that the hand lever is used to relieve pressure (from the big spring underneath) whist loading the part to start whatever.

Hope my musing makes sense to others

Bob D

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