Yet another Quorn

[Charles Lamont]

I have also started work on several other castings. The toolholder and spiralling arms both have machined front and back faces, square and parallel, but not to finished sizes.

Clamping the toolholder arm in the vice for initial clean-up cuts did not yield faces that were parallel or square to the cast body, so I had to redo one face with the arm clamped to an angle plate (poor focus) and use that as datum for the other side. (The marker pen symbol on the vice is to remind me it has not been squared up.)

The tooth rest collar is a minor landmark as the first casting to be finish machined.

[Charles Lamont]

Enough of the cast iron for now.

After making a start on some of the turned steel parts, I decided to have a brass session. Among the various jobs I tackled was the Tilting Bracket, which I will go through in some detail as it is a tricky little job.

After careful measurement and planning the sequence of operation, I filed the few lumps off the back of the pointer finger. This is a clean flat surface that has accurately cast geometry in relation to other surfaces and will not be machined, so I used it as the first datum surface, setting the top of the casting level as a first guess, and took a cut over the top sufficient to clean up.

Next, using the top as a temporary datum, I set the casting in the machine vice, top against the fixed jaw. The 'tower' and the arc piece ('battlements'?), which forms the stop faces for the Rotating Base, both have very little spare metal and needed to be adjusted on packers and shims to correctly level the two. Milling the front face of the finger, enough to clean up most of the surface, establishes a vertical plane. I also temporarily faced the clamping lug for marking the hole position, and drilled and reamed a temporary clamping hole as close to the pivot point as I could get it at this stage.

With the front face clamped to the milling table I could take a cut to clean up the boss at the back.

After a little filing to clean up the sloping sides of the pointer finger I set it up on an angle plate with equal angles measured each side of the pointer to get it vertical. I want the finger tip as broad as possible as I am hoping to be able to engrave it with a vernier scale. In this position I could now take another cut sufficient to correct the top surface plane.

At this point the casting had two geometric datum planes fixed, and the next job was to finalise some dimensions. I took the casting and angle plate to the surface plate and made four sheets of sketches, taking more than 20 measurements, mainly with the height gauge. I drew it all   in 2D CAD. Armed with this, I could decide where best to find the part inside the casting. It turned out to be generally pretty accurate, the biggest problem being the clamping lug which is rather lopsided. As I am using pad clamps that need a 1/2" hole, rather that the 5/16" hole used for the original split casting, this is going to result in less wall thickness around the hole than I would have liked, considering the considerable bursting forces that the clamp pads can exert on their housing. The last photo in this group shows how it was marked out for the pivot and pad holes, using a plug in the hole already made. I think I must have staged this shot, as the holes are already centre popped.

[Charles Lamont]

Next, the job is set up on the faceplate for boring the pivot hole. The revised design for this now has a taper seating both sides so that the assembly is more firmly clamped, with a smaller parallel bore between the two tapers. Having finally persuaded the the centre pop to run very nearly true, using a wobbler and DTI, I pulled the single clamping dog up hard and then carefully balanced the job with my faceplate balancer. The bolt just showing behind the casting is there just for balance. In vindication of the use the balancer, I was able to run this set-up at 1000 rpm without vibration.

I faced the back of the boss to size and, as there was already an off-centre hole, I started to open the bore up using slot drills rather than twist drills, then bored it true before finishing with a tapping size drill.

I then bored the taper, realising early enough to reset the topside to 15° instead of the 20° I had started with. The original design (as revised) calls for a 40° included taper. I cannot think why, apart from that the Prof seems to have standardised on that angle. A shallower taper will clamp better and will still be self-releasing. I have revised the revision and settled on 30° included, and increased the diameter a tad to boot. There is still plenty of meat round the hole. I had already made the clamping bolt with its tapered seating to use as a gauge, and tweaked the topside angle until the hole blued up properly.   

A useful idea from the Mark 3 is to tap the central hole so that the part can be mounted on a stub mandrel for boring the second taper seating.

[Chipswitheverything]

Your full write up of the work on this component will be helpful to prospective "Quorners" , if such there are these days. Perhaps the Hemingway revision of the package will have generated a new interest in the Quorn, though there must be many around in workshops already.  And a lot of half finished ones!, as mine was for so many years ...
 I did the pad clamp modification, and the taper seating when I machined this bracket, and it all works securely.  Perhaps one can fairly say, that if one can sort out this awkward casting, then most other castings will not present much worse in the way of holding conundrums ...  Dave

[Charles Lamont]

Making the clamp hole was simple enough to do with the casting bolted to the milling machine table. A 3/8" drill with its cutting edges ground for zero rake went through nicely. On opening out with a 15/32 drill which had not been 'dubbed', it grabbed ferociously, twisting the casting round on its mounting bolt. It also pulled the chuck off its taper arbor, which may have saved things from worse damage. Hmm. Plan B required.

After mulling it over for a couple of days and doing a bit more work on some garden gates, I set the casting up on the boring table, using the clamping bolt in the chuck to position the casting and then offsetting the table as before with the Wheelhead Collar. I gingerly bored the hole to a working fit on 1/2" silver steel. The photo shows the patch of marker ink that was left after boring.

With the job set up the other way round, I bored it enough to clean up: 0.534" diameter for 3/8 depth. I made a sleeve to fit, using a piece of phosphor bronze that was not at all keen on being machined, Loctited it in, and put a 1/2" reamer through by hand to finish.

With that sorted, it was back to the surface plate to mark out for the vertical hole. An L-shaped piece of aluminium plate allowed me a secure mounting on the angle plate. (There are nuts securing the ally plate to the angle plate while allowing to casting to be adjusted before tightening the strap.)

 

[Charles Lamont]

With the job set up and almost ready to go, I thought I had better check for square. (The first photo actually shows a final check, but illustrates the method.) It was a bit out. A shim under the angle plate put it right. (This photo was actually taken at the end of the job.)

The third photo shows the centre pop being set to run true using a spring-loaded wobbler against the tailstock centre.

Next, with the job running true, the faceplate has been transferred back to the faceplate balancer and the balance weights added and adjusted.

Meanwhile, I remembered that, unable to think of any other way to measure the 1-1/2" inside radius of the stop arc, I needed to make a gauge for it. It is 3" diameter, and has an accurate 1/2" hole in the middle.

Lastly, all the machining at this step is done, with the hole bored 1/2", the top faces finished to the correct heights, the 90° taper turned, and the inside of the stop arc machined to clear the Rotating Base. A bit of the mounting plate got machined away, and the brass blank for the clamp pad has been removed for inspection.

[Chipswitheverything]

Almost there on this awkward component. There are times during the bolting up and packing when to have several extra arms and hands, like some Gods, would be rather helpful ...  I had already made the rotating base when I tackled the radius on this casting, so had the guide to the size.  Dave

[Charles Lamont]

Next, I milled the bottom face to size. Then I turned the temporary holding flange off the clamp pad blank, and split it. I used the pads to clamp the casting to a piece of bar in the lathe chuck. This allowed me to cut the relief in the back of the finger and very lightly face a bearing surface for the retaining washer that holds the Rotating Base in place. I also machined the outside radius of the stop arc, and, for aesthetic purposes, a slightly coned underside and a series of chamfers on the corner, which will be blended to a radius by hand.

With the stub mandrel made, the casting was fitted onto it and the finger front faced to size. At the tip, the radius and a bevel will need to be done later. Finally, I bored out the front tapered seating. That is as far as I have got with this bracket, but there is more work to do, mainly the crenellation of the battlements to form the radial rotation stop faces on the merlons and the central embrasure for the index line. By the time I get there, I may have come up with more metaphors from the terminology of mediaeval fortification architecture.   

[Chipswitheverything]

Well, at least all the "murder holes" have been created now .... Dave

[rklopp]

"...but there is more work to do, mainly the crenellation of the battlements to form the radial rotation stop faces on the merlons and the central embrasure for the index line."

I'm a big fan of big words, but need help on this one...:-) Please translate.

[crueby]

"...but there is more work to do, mainly the crenellation of the battlements to form the radial rotation stop faces on the merlons and the central embrasure for the index line."

I'm a big fan of big words, but need help on this one...:-) Please translate.

Translation: needs fancy stuff like at the top of a castle tower!      Time to go re-watch Monty Python And The Holy Grail!   

[Charles Lamont]

This may help:

[crueby]

Thats a very complex part!

[Charles Lamont]

Perhaps the most drastic modification I am making to my Quorn concerns the belt drive.

Firstly, I liked the idea of being able to run the spindle at a higher than normal speed. The Prof shows a large laminated wooden motor pulley capable of driving the spindle at 15,000 RPM. I thought I might be able to work in something less cumbersome.

Secondly, although the round belt is no-doubt perfectly adequate, I just felt it was a bit crude. Now, an early example of the Quorn was made by Neil Hemingway (of Hemingway Kits), and he used a poly-V belt (J-section, I think). A photo of it being used as a toolpost grinder appears towards the end of the Quorn book. Turners even used it a one of the montage of photos on the cover of their Poly-V brochure.

I found that by using the less common H-section poly-V, I could get a 2-speed drive inside the belt guard. However, an aspect of the design which caused me a great deal of head scratching, was how to implement a reasonably easy way of tensioning the belt. The original arrangement of sliding the slotted motor mounting plate on its three mounting bolts was a non-starter. All these bolts also serve some other function. Besides which, I wanted to extend the motor plate to encompass the spindle housing, the better to keep grinding dust out of the drive. I fiddled about with an eccentric mounting for the motor, but eventually gave in to the idea of trying a jockey pulley.

The design manual tells you not to use a spring tensioned jockey pulley on the tension side of the belt, but as the Quorn needs to run in both directions that is is out of the question; it has to be positive in action. After much doodling in AutoSketch, I eventually managed to squeeze in a mechanism that would do the job, and then realised that it was the same cam-operated arrangement as used on my lathe. To get stable quiet running, the jockey pulley is mounted on two ball races, with a wave washer to provide a light axial preload.

The jockey pulley is close to the minimum recommended size for running on the back of the belt, but the smallest driven pulley is comfortably larger than the minimum. The pulley ratios give nominal speeds of 4500 and 8000 rpm. The pulley sizes were calculated by using an Excel spreadsheet to calculate the trigonometry and using the goal-seeking function to adjust the pulley diameters to arrive at the correct belt length for each ratio. The resulting drive parameters are comfortably within the manual's design envelope. (And the envelope of the drive within the belt guard.) It remains to be seen if in practice the belt really does tension equally in both positions (but if not, pulley diameters can be tweaked). I have the belt in stock, and as a result of forgetfulness, three spares.

Wanting to see what it would look like, and while having a brass-shop session with the Tilting Bracket and some other bits and bobs, I started work on the fabricated brass belt tensioner arm. All the other tensioner parts seemed to get made before the arm was finished, mainly as silver soldering is not my favourite job, and I needed to devise a jig to hold the four pieces for soldering.

[rklopp]

Charles,

That is top tier craftsmanship. My hat is off.

RKlopp