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Member postings for Dr_GMJN

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

Thread: Stuart Twin Victoria (Princess Royal) Mill Engine
10/05/2021 22:08:08

Thanks both.

Got the holes drilled and counterbored tonight; they all match - so far.

Very easy to get them mixed up, I’ll have to keep the markings clear to prevent a time consuming mistake.

Still have to drill sockets for the linkage bosses in the inner walls (B & C), then we will see if the 3D printed casting draft jigs work...

09/05/2021 21:21:58

So it’s the one year anniversary of starting the 10V, so I made a start on this one. This time with some help from my son:

We got the castings and bed material out - shows how much work this is going to be:

After re-figuring out how all the 3D printed jigs were supposed to work, fist job was to trim the bed plate sides to length on the mill:

Small start, but it’s a start.

Next job is to co-ordinate drill the counterbored holes.

12/04/2021 22:03:25
Posted by Ramon Wilson on 12/04/2021 20:48:11:

Hi Doc , been out of it for a few days (plastic distraction) so only just caught up with your progress. Nice work on the boring bar and you initial tool grinding. You might find a holder made from round bar more beneficial in creating angles but those you've got so far look just fine. I would use the sharp tip as per the last image for getting under the skin but for a really good finish 'off the tool' on the last ten thou or so I'd grind (not file) a nice radius on that corner.

Keep the speed and feed well down for best results.

Looking good - go for ityes


Thanks Ramon. I’ve taken a week off work for gardening and changing the rear brakes on the car. Unfortunately the easiest way to change inboard brake callipers is to remove the entire IRS. Got it removed today with the boy helping, next up is swapping the pots and re-fitting without getting squashed.

After that’s done, it’ll be full steam ahead on the P.R., although I’m still battling with an Airfix Swordfish. Shame they decided to put a massive pocket under the upper wing, that results in some subtle but very difficult to remove sink marks. It’s already been in caustic soda once...

Edited By Dr_GMJN on 12/04/2021 22:15:04

12/04/2021 20:00:24
Posted by JasonB on 12/04/2021 06:57:17:

I don't round mine.

Yes once you are close give it a lick with the diamond so it's good and sharp for the last couple of cuts.

Ok thanks.

11/04/2021 21:08:18


when filing the edges, am I aiming for a sharp angle, with no edge or tip radius at all?

Also, how long will the bit stay sharp? Should I re-file it after every cut, or perhaps before the final couple of cuts?


11/04/2021 17:23:12

OK thanks Jason.

So I'll make a couple more for good luck, touch the edge up with the diamond file, and also grind them to the correct length.

On the last photo I posted, should the tool be rotated anti-clockwise slightly? I noticed the flat behind the cutting edge was angled down in the grinding drawing, but obviously you can orientate it how you want in the bar.

Just got to do some car work this week, then I can finally make a start on this one.

11/04/2021 13:09:25

So I 3D printed a grinding jig, which I temporarily fitted in front of the bench grinder. I've graduated the angle markers at 10 degrees (they still need filling with white Milliput), and I'm hoping absolute accuracy isn't essential for this:

Is it acceptable to use the side of the wheel for grinding? If not, I think I need to make another recess in the table 90 degrees to the existing one.

Also made a holder for the 6mm diameter bits that Ramon sent me - my fingers were getting burned without it:

I have followed Jason's diagrams, but I'd like some comments on accuracy, surface finish, whether it needs a tip radius, whether it needs further finishing with the diamond files, or anything else that's relevant. I've never ground tools before, and don't want to ruin a casting through not grinding the them accurately enough. Here is where I am:

Have I ground this in the right orientation? The intention was to set up as shown, and move the cylinder on the cross slide from left to right (chuck would be on the left of these images:

I'm not even sure how the tool should be orientated in the bar, and which surfaces are is doing the cutting! Does centre height setting apply to this method, if so, how to you adjust it? As I said, any and all advice gratefully received.


Edited By Dr_GMJN on 11/04/2021 13:10:51

Thread: Home Made Rear Toolpost Issue
06/04/2021 22:53:43
Posted by Howard Lewis on 06/04/2021 21:34:24:

Use of slips depends on your background, and the standards you set, (Even, if my case there is great difficulty in working to them ).

Having spent the major part of my working life in Quality and therefor spending a lot of time with Inspection, Standards Room and Calibration Room, I am obviously biased.

Can anyone say why, if they are so useless, Industry uses slips?

If they wring together the condition is good enough to say that they are accurate. Even if they don't, but have no obvious damage, they can be used as standards which are far more accurate than anything else in the usual hobby workshop.

I last used mine (Which are old and some do not wring together ) to measure a lipseal OD and the bore for it, so that the right interference could be accurately achieved.

Before that, to ensure that a there would be the required interference on a "Heat and Freeze" assembly, when cold..

Each to his own.


Not sure anyone said they were useless. It's just that - for me - a second hand set of slip gauges bought off EBay is far more use for different sized, flat weights for model building, or packing pieces for setting up work, than for the high-accuracy metrology work they were intended for in industry.

It's nothing to do with the standards I set for myself, just that its not worth the bother of using them with the care they demand, in my workshop/garage. For example - is your workshop temperature controlled to 20 degrees C +/- 0.1 degree? Do you use chamois gloves to handle them?

It's not like I deliberately throw then on the floor or dip them in salt water, and I'm happy to use some odd ones to check that a micrometer or vernier is about right, but that's as far as it goes. The stuff I'm doing doesn't seem to require absolute precision, so long as things fit together nicely and don't rattle, I'm fairly happy.

Don't get me wrong - I'm not some caveman, and I do look after my tools as best I can, but when equipment starts to take more effort to use correctly in a home workshop than the results justify, frankly, what's the point?

Thread: Stuart Twin Victoria (Princess Royal) Mill Engine
06/04/2021 19:47:17
Posted by JasonB on 06/04/2021 07:46:25:

You can do it either way but having the section of bar true to the axis means it's there ready to make use of, also some of my bars are from quite rough hot rolled material so you would be measuring on an uneven surface which won't be very consistent.

As for overlength bar I sometimes drive with the chuck and just support the tailstock end with the ctr so you can put more of the bar into the chuck if it's too long but it does save having to keep making bars when the next longer job comes along.

Ok understood, thanks.

So this is the first attempt. I did shorten it a bit - I can't see doing anything longer than the P.R. cylinders, and wanted to maximise stiffness. I've still got a couple of inches each side of the cylinder to play with:

I didn't have a 6BA tap, so used 7BA for the adjusting screw instead. The locking grub screw is M5 - might need turning down a bit because I think it will touch the bore as it is. The tool hole is drilled at 6mm, and the spare stubs that Ramon sent me are a snug fit in it. The adjuster thread is 4mm long, the tool bore 14mm long. I did turn the middle true - it wasn't really out at all, and I'm not particularly proud of the finish I got, but I don't suppose it matters. Also milled the flat for measuring, and another for the carrier:

I also found a 3/4" carrier in a box of stuff I got with the lathe, which cleaned up nicely. If it doesn't work at least I've got a nice steam punk hammer:

Now to grind a few tool bits. I'm wondering if I should make a grinding holder for them out of perhaps square bar - I think holding by hand isn't really on, and grips might burr the surface such that it might not fit in its socket?

Thread: Home Made Rear Toolpost Issue
06/04/2021 13:29:21

Thanks guys - a few points, which to be fair I did mention in various posts:

As I said, some types of PVA are water soluble, and again, I said I removed it from the slip gauges by soaking in warm water.

I did mention that the tool projection was excessive in the picture (can't remember why, but that's how I'd left it), but the tool post is often turned at an angle, so even with reduced overhang, the gap is representative - and it's not nice to be constrained between two immovable objects while machining.

I also mentioned that I'd used a socket wrench to re-tighten the M8 capheads, and that opening up isn't an issue now. Regarding parting off on brass - I figured that if it wasn't working properly on brass, it sure wouldn't on steel. I'd rather do the setting on easier to machine materials. I'm waiting for some longer M5 clamp bolts to arrive, on which I'll remove the end threads and face the ends.

And yes, the insert is profiled to curl the swarf with a central bulge - they work well, but because they are asymmetric, it's making height setting a bit more difficult. The blade holder also tends to spring away from the workpiece at the final bit of the cut, which itself leaves a pip. I'll sort it eventually.


05/04/2021 23:32:05

Re. the toolpost being left in-situ, and the front clamp causing an obstruction:

This is a top view of the lathe showing the front toolpost, and rear post turned 90 degrees. The front post is usually angled a bit, and the tool not extended as much, which makes the relative clearances shown fairly representative. You can see that there is not much room with the rear post in place, and it’s far less risky and stressful to simply remove it:

Likewise in this image you can see that the front clamp is not in the way of the workpiece - still room even though I don’t envisage turning parts any bigger than that shown, at least not outside the gap:

05/04/2021 22:41:57

So the largest diameter I can envisage parting in the near future is c.42mm cast iron, for steam engine cylinder caps. By pure dumb luck, the projection of the blade is just enough, plus a bit, for that. So once set by trial and error, that will be it for the rear post.

For turning tools, I can imagine spending hours making a setting gauge, then ending up re-setting by trial and error anyway, depending on tool projection, workpiece overhang and material type. Maybe I’m being defeatist, but most fettling I do on the lathe (eg tailstock alignment) seems to end up in a compromise due to inherent wear. I can’t see tool height being any different.

05/04/2021 22:27:48
Posted by Grindstone Cowboy on 05/04/2021 22:20:00:

frown Hopefully tongue firmly in cheek

Nope. I bought them solely for the purpose of weighting down decks and other parts of card ships while the PVA sets. The different sizes are handy to fit between various stiffeners and bulkheads. I bought them a few years ago off Ebay for £30. Incomplete set, and I have no idea of their accuracy, so wouldn’t trust them to be used as intended anyway. Some wring together, some don’t. They do come in handy for general use as parallels/packers though - accurate enough for the things I’m doing.

OK the Brillo pad was a joke - I use water soluble PVA so just dunk them in hot water ha ha.

05/04/2021 22:13:43
Posted by Howard Lewis on 05/04/2021 18:51:29:

Slips are accurate to millionths of an inch, so no need to risk damage by not using the protectives.

If scratched, or worn, they will no longer wring together, and then be difficult to stack for other dimensional checks.

Not sure that using for direct measurement on a machine is really a proper use for them.


Thanks Howard,

I’d have to get rid of the PVA glue off them first - I find a Brillo pad is quite effective for this.

Thread: Stuart Twin Victoria (Princess Royal) Mill Engine
05/04/2021 21:19:05
Posted by JasonB on 05/04/2021 19:13:13:

As you will need to set the tool to desired radius plus half the bar diameter turning the area around the hole true ensured that the half diameter is actually half diameter not what half the bar is from the lathe axis.

I think mine have a length approx equal to the bar dia turned true equalised about the hole

Edited By JasonB on 05/04/2021 19:14:40

Don’t you turn the bore until it cleans up, measure it, and increment the tool outwards by half the difference to final diameter? I can see why a flat would make tool extension measurement more accurate, but not how turning cylindrical would help, unless it’s for absolute rather than relative measurement?

05/04/2021 19:00:50
Posted by Ramon Wilson on 11/11/2020 08:40:15:

A simple pin set on centre line of the arc and another in the cylinder wall will locate the feet accurately enough while the JB sets, though I was underr the impression the mating area was going to be machined too.

Yes another way this op can be done, but as Jason says it would be best to machine the lower surfaces after bonding - done with the cylinder held on a mandrel the dimension would be both identical over both parts and importantly parallel with the cylinder bore too

You can make a simple 'tween centres boring bar of any size you want to suit the job. I have some made many years back from silver steel. They have a small flat on them where the cross hole for the 1/4 HSS cutter goes. By making the hole blind the flat area can be drilled and tapped for say a 6ba screw which helps move the cutter when very small movements are required. Remove screw, mic across flat and tool tip - simple maths gives the radius. There are other ways - inset adjustable carbide tips for instance but that above has served me well for a long time now - I much prefer to use 'between' centres for bores to eliminate taper.

Soft solder will be sufficient!


This pic should help explain it better. The turned portion is to ensure the diameter is true to the axis of the centres. Radius required is dimension plus .462 across tool tip and flat


Edited By Ramon Wilson on 11/11/2020 08:52:42

I’m making the bar at the moment - what is the purpose of locally turning it true? I can see that it’ll give a co-axial cylinder where the tool is, but a

I assumed you’d machine, measure and re-set the tool. I can’t figure out why you’d need a cylindrical portion of the bar?

Also, I think I’ve cut the bar too long. Presumably it should be the minimum length for the job plus a bit - but how far each side should the ‘plus a bit’ be?


Thread: Home Made Rear Toolpost Issue
05/04/2021 11:07:35

Ok thanks guys. So I could make a gauge similar to Johns. To get the height, perhaps put some bar in the chuck, then measure the height by putting slip gauges on the cross slide, then add the radius of the bar? Then machine to that dimension? I don’t have a height gauge, but have got most of a set of second hand slips.

04/04/2021 22:01:39
Posted by old mart on 04/04/2021 21:53:29:

You could get a lathe tool set to cut exactly on centre and then make a gauge that sat on the bed to match the height. A very useful gadget.

What's the difference between that method and using a dead centre? Aren't you still judging it by eye?

04/04/2021 21:46:45

Determining centre height to that degree isn't something I could do. I'm currently setting tools initially be eye against a dead centre, then by trial and error to home in on not getting a pip. Pretty tedious.

04/04/2021 20:52:53

Thanks Howard - there's a picture on page three, third post down, that shows that there/s no room for a turning tool, a workpiece and the rear post.

I understand the clamp force comment, but it also requires flat mating surfaces to give the optimum stiffness. I can't guarantee this, so the extra clamp provides some backup, and it's not in the way of anything.

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