By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Stuart Twin Victoria (Princess Royal) Mill Engine

All Topics | Latest Posts

Search for:  in Thread Title in  
Dr_GMJN05/04/2021 21:19:05
avatar
996 forum posts
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?

JasonB06/04/2021 07:46:25
avatar
Moderator
20443 forum posts
2267 photos
1 articles

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.

Dr_GMJN06/04/2021 19:47:17
avatar
996 forum posts
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?

Dr_GMJN11/04/2021 13:09:25
avatar
996 forum posts

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.

Thanks.

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

JasonB11/04/2021 15:02:07
avatar
Moderator
20443 forum posts
2267 photos
1 articles

Looks about right.

Just make sure that the bottom of the tool arrowed in blue does not rub against the edge of the hole

docs tool.jpg

Its the arrowed edge that does the cutting and that's the one you could give a run to with a diamond slip

docs tool 2.jpg

Best to avoid using teh side of teh wheel if you can

Dr_GMJN11/04/2021 17:23:12
avatar
996 forum posts

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.

JasonB11/04/2021 17:33:00
avatar
Moderator
20443 forum posts
2267 photos
1 articles

Yes you want the top face sloping down slightly from the cutting edge as shown in green but make sure the red clearance angle is not lost as you rotate it, you want both to be about 5degrees

docs tool 3.jpg

Dr_GMJN11/04/2021 21:08:18
avatar
996 forum posts

OK.

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?

Thanks.

JasonB12/04/2021 06:57:17
avatar
Moderator
20443 forum posts
2267 photos
1 articles

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.

Dr_GMJN12/04/2021 20:00:24
avatar
996 forum posts
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.

Ramon Wilson12/04/2021 20:48:11
avatar
1077 forum posts
219 photos

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

Ramon

Dr_GMJN12/04/2021 22:03:25
avatar
996 forum posts
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

Ramon

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

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
cowells
ChesterUK
emcomachinetools
Eccentric July 5 2018
Warco
JD Metals
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest