Turning a cylindrical bar into a semi circular cross section bar?

Yes I should have read the advert properly I assumed it would make a good stater project. Thank you for all of your suggestions I did consider filling, but felt that this would defeat the object of the exercise. Because I am just starting out again I don’t have any scrap off cuts, but I have now bitten the bullet and bought some stock bar, it’s going to pain me to cut bits off for off cuts!

here’s a question, how would I make a 90’ groove along the length of my off cut to make a small V-block to add a bit more support when facing off my cylinder?

Edited By Paul McDonough on 04/03/2023 08:55:40

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It’s probably a bit late to mention it … but :

In the absence of suitable tools … making a 120° groove, by fixing two lengths of hexagonal bar together, would be much easier.

MichaelG.

Very true but you have to be reasonable as to how large a step there is between what a beginner already knows how to do and what they need to learn for the next job. Too big a step or too many steps leads to, at best, disillusionment with unattractive results and all too often compete failure. Too much of that and a new hobby will be sought.

Unnecessary multiplication of complication, whether in design, construction or work holding should be avoided wherever possible. Which goes in spades for novice projects. That half circle part is tricky problem in work holding that has no place in a project intended for the inexperienced. There are so many ways it can go wrong. Certainly way too much trouble for pure cosmetics.

I would obtain a piece of 5/8 x 5/16 flat bar and reduce it to whatever shape seems pleasing. Whether using a longer piece and turning it half circle as suggested in my previous post, filing the corners taper or simply radiusing the edges. Option 3 for me!

With the blank prepared mount it in the four jaw chuck with the flat face hard against at least two jaw stops so the basic slot shape can be produced by drilling a line of holes. You may need a scrap behind the job to keep the drill away from the jaws. The easy way to get the sideways step is to use a scrap of material as a setting gauge. Loosen one of the jaws holding it longways, insert the "gauge", bring the jaw back to lightly touch it, remove the gauge and use the opposite jaw to push the part over so its gripped ready for the next hole. Loosen the short ways jaws a touch so it slides without rocking.

Drill alternate holes so the is a gap between the holes drilled in the first run. Start with a centre drill to give a decent lead in. If the web between the holes is significantly smaller than the drill diameter find something to make decently fitting plugs to help keep the drill true. Brass would be best but alloy, steel or even JB weld will work. As ever with brass the drill needs to be decently sharp.

If you do decide to make it half circle as per plans first file a flat almost as wide as the slot will be so the drill has a nice clean start. Brass is skiddy at the best of times. Starting on a curved surface is an open invitation to trouble. A three flute centre cutting end mill, such as the old Clarkson throw-away series would be better than a drill for producing the the holes. Probably too short to go right through in that size but one will give a nice clean round guide hole most of the way through to finish with a drill.

Clive

You can hold the piece of square bar in the toolpost, packed to suitable height, and machine a groove down it with a 90 degree cutter such as a countersinking cutter held in the lathe chuck.

Looking at the part and what it does I would say it does need some accuracy and not everyone could file to that accuracy including me.

Any slight height deviation between base and crankshaft bearing or angle and the hole in the standard that this piece supports won't line up with the hole in the outboard crankshaft bearing support.

My current thought is to clamp horizontally to the topslide across the lathe and pack it up to ctr height. Mill out the slot. Then mark half way point around the part and saw off most of the waste material then it can be soldered to the standard. Finish by clamping the standard to top or cross slide and mill/flycut to final size this should ensure it is at right angles to the flat standard and height is easy to measure and no risk of it being off if something moves during soldering.

As for the Vee using the offcut from the base mill that first with the corner of a milling cutter and position the Vee so it is in the bit you saw off. Mount using the two edges of the vee to set it level and mill the sawn surface flat.

Hi Paul, further to Clive Foster's idea, you could buy a piece of 3/8" x 3/4" from say macmodels.co.uk, cut two pieces long enough and mount them in your four jaw as shown below, but making sure the centre of the two pieces are central to the spindle axis, drill and tap a small hole in the end sticking out but making sure they are both nipped up to each other and screw in a short grub screw, this will stop the two ends parting away from each other during turning. Put a small centre on the joint for your tailstock centre, and then turn the two pieces down to size. Once turned down, just cut to length. You will then have two pieces of half round, so if you mess up the first attempt of putting the slot in, you can have another go with the other piece.

Regards Nick.

Excellent, Nick

A real case of “If I were you, I wouldn’t start from there”

… that’s ‘Engineering’ !

MichaelG.

+1 for Nick's method. You could also soft-solder the mating flat faces together for more security.

Yup, starting with two rectangular bars softsoldered together was suggested to me by a friend I felt it was cheating!

but thank you for the suggestions and the very helpful images.

this reminds me, how do you post images on this forum please?

As for starting from the wrong place, yes that does seem applicable I should have started with another kit! LOL!

Although thetwo flat bits is a way to do it it does seem to defeat the idea of buying a "kit" of materials in the first place and does not really address the issue of soldering the part on exactly true and suare to teh vertical standard.

So putting my metal where my mouth is this is how I described in my previous post and answers the question of how to make the part with the material supplied.

First face the two ends of the bar

Clamp to topslide with packing to bring it upto ctr height. If your toolpost will take 5/8" than you can just hold it in that. You can then drill your series of holes

Or better still mill the slot

Saw roughly in half to get rid of most of the waste

Solder to the vertical member

back to the lathe and clamp it by the standard clocking that true along the lathe axis and flycut the end back to half the 5/8" thickness

Job done, if you don't have a fly cutter or big milling cutter try this

Wow, thank you that is truly commitment to helping out!

thank you very much.

Hats off to Jason B for ILLUSTRATING the full chapter and verse.

That said the standard of design on so many "beginner" designs is very poor and turns the project into anything but beginners work. Add to that castings that hardly ever include chucking or clamping pieces or sit down pieces and you have a supply industry doing it's level best to strangle our hobby. It makes me so annoyed.

I think JasonB might feel the same way given his re-working of old designs that are designed to be MADE.

Martin

Just wondering why it is being suggested to waste material by turning two pieces of flat bar when one could be done on it's own in the 4-jaw?

Btw I would not have thought of putting a lathe tool in at chuck and using it like a small fly cutter

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I assumed it was to allow the use of a tailstock centre for support

… very wise, given the small chuck that Nick was illustrating.

MichaelG.

Edited By Michael Gilligan on 04/03/2023 17:36:53

Hi JasonB, OK yes there is a bit of waste but you do get two pieces to play with, whereas cutting the the bar in haft produces a bit of waste that wouldn't be any good, should the piece that has been turned to size goes wrong. I'm not saying that my idea is any better than the one that you have shown, and I understand your method, and it is a valid one, but I don't know if Paul has the equipment or the skill to do it the way you have shown. Of course with the way I've described, there is no heating involved or cleaning up once finished. Although I thought of it before reading Clive's method, using the two pieces will allow tailstock support. Now by all accounts, looking at the finished engine, it seems to me that the semi-circular piece will need a couple of tapped holes on the flat side to fix it to the base, which could be drilled easily on a bench drill before the two parts are turned together, and can be used to hold the piece in a similar manner to the way you have shown, when milling the slot. My method was only an alternative way of doing the same job, and many others my find an easier way for them, There is waste, but it's a small amount compared to videos I've seen of things milled out of solid blocks of metal. There is always a cost in any method, whether it's extra material, heating, cleaning, time mistakes, etc.

If Paul does it by the method I've described, and it turns out fine, he could always buy another kit and make another engine and then sell it for a little profit to put towards his next project.

Regards Nick.

As for wasting half the round bar by sawing it off yes but it is better than wasting it all by not using it

As the base and standard are going to be soldered together then there is no extra clean up with my method as it will be needed anyway and I'd be happy to do the same if it were JBWelded or soft soldered together.

And apart from a bit of bar for a clamp (which I have said may not be needed) and some packing no extra equipment needed

Did not add too many photos but my setup also allows for drilling and tapping the two holes in the base perfectly perpendicular and just about exactly spaced by use of the cross slide handwheel.

But above all it ensures the base is true to the standard. other methods being suggested hope that the stitch drilled and filed slot will hold the standard truely vertical.

Cash could also pay for the additional materials bough

Edited By JasonB on 05/03/2023 07:23:00

Unless you drill and file the slot, then solder the two pieces together, then machine the flat on the round bar, either as shown in the pic above or by holding the standard in the four jaw and taking a facing cut.

As with most machining, there is no end of different ways to skin the same cat.

Edited By Hopper on 05/03/2023 07:37:29

Exactly Hopper which you can't do if the finished bottom of your round bar is one flat face of the rectangular bar being shown. You have to hope the slot is true and that the jointing of the two parts is also true.

Edited By JasonB on 05/03/2023 07:59:24