Member postings for Jon Gibbs

I'm coming to this thread late, but the OP asked what's the point of slow speed grinders for woodturners?

I am a model engineer and a woodturner and have a Creusen slow speed 6" grinder with two 40mm wheels and like it very much.

The reason for me is that I can touch up my tools in a quick but controlled way. I tend to use a homemade jig system for all of my w/t gouges and this allows me to resharpen half way through turning something. If turning exotic and abrasive timber it may be necessary to be resharpening every few minutes.

A standard grinder would work, but it's very easy with small gouges and fine edges to blue the HSS. In theory this does no harm but IMO it's better not to if you can avoid it.

A 60 grit wheel on one side is still quick enough for rough shaping and a 120 grit fine wheel is great for frequent touching up with minimal loss of steel. The Creusen is very nicely balanced and quiet.

Old Harrison lathes have that nose thread - both engineering and wood lathes

Jon

That sounds remarkably familiar.

I ordered a set of carbide threading inserts and a holder from China, all for the bargain price of £11 including postage - crucially under the £15 import duty threshold. The jiffy bag, complete with a gaping hole, made it all the way from China into my postbox, but Evri still registered it as delivered - the courier can't have failed to notice the envelope was empty.

The bay seller was extremely good about it though. I sent them a photo of the envelope in a message, explained what had happened and asked them to please resend the item in better packaging. They were very obliging and I received the replacement two days ago, in a plastic rather than a paper envelope. It earned them a flawless review, naturally.

As for Evri...

Thanks Clive, that's what I thought but I think I was obviously at cross-purposes because I was thinking partial profile inserts whereas you were clearly thinking full-profile.

...and I think your last paragraph, which I think probably also applies to partial profile inserts, means we may be in agreement over the big advantage of Martin's parallel top slide method.

Many thanks

Jon

Forgive me. I've read through Clive's Zero-to-Zero technique description several times and I can see that it'd result in a workable thread but isn't there a danger that the minor diameter might be cut too small by over-depthing creating a sharp valley, or have I missed something?

Is that what you meant by the "PS Don't even think about allowances and tolerances!"?

I'm a fan of the alternative approach advocated by Martin Cleeve of setting the top slide parallel to the lathe bed and, after the theoretical depth is reached plus a small allowance, broadening the thread groove until a good fit is achieved using the top slide.

Jon

Edited By Jon Gibbs on 06/11/2022 13:06:02

Blimey this is a blast from the past - as a Scout we used to use similar triangles to estimate the height of trees.

If you position a vertical pole 11 horizontal units from the base of the mast and sight from the ground a further unit away from the pole, the intersection of the top of the mast on the pole allows an inch to feet conversion - one inch on the pole = one foot on the mast.

Edited By Jon Gibbs on 09/07/2022 20:35:55

I use end-feed Yorkshire straight pipe fittings cut in two with a hacksaw and then retrued once supported on the wooden handle. Another advantage is that the internal diameter is standard.

Jason, I used a 45mm diameter saw on a 25mm (outer edge) diameter arbor.

So, it was fairly well supported but with 10mm unsupported I'm sure it could still flex.

Thanks Pete.

I remember seeing your table now but didn't see the significance - sorry. I was swayed by the discussion about sizing the blank for an extra tooth which obviously adds 0.050" for 20DP.

I'm new to gears and so clearly making it up as I go along

Thanks Pete.

I didn't know about the correct shift .

I just rounded up the dimensions from this thread... **LINK** to add 0.050" extra. But, as you say, it doesn't matter a jot because of the banjo adjustment.

I know this is quite an old thread but I've been after a 12/25 slow feed cluster for my old ML7 for quite some time and too mean to pay the £40 Myford charge for a factory made one or for a gear cutter for that matter.

So, I thought I'd give this method a go for making a 20DP 12 tooth gear out of cast iron on a 5/16" keyed shaft so I can use the 25 tooth gear from the change wheel set. I was pretty hesitant having read Jason's comment but thought the only way to find out for sure was to try it.

The spreadsheet from Andy's YouTube channel has an imperial sheet and a quick hack of the page allowed me to add .050" to the diameters to reduce the undercutting and provide more clearance on the 3/8" shaft. I used a small .032" thick slitting saw which is slightly thicker than the value recommended which would be about 0.63mm. I didn't notice much flexing in the saw since the cuts were pretty light after the first two which excavate the majority of the waste.

Anyway, it seems to have worked well. I now have a gear which meshes well with the larger gear it drives in the chain and I now have a working slow feed.

As mentioned above, it's not the fastest method but it does work even for relatively small gears. It's also obviously very low cost.

Edited By Jon Gibbs on 08/06/2022 18:07:39

No it's not a left hand thread. At least I removed mine yesterday and it was a right hand thread.

Jon

This guy's quite a good YouT presenter on blacksmithing stuff and anvils...

**LINK**

Just finished making and fitting some new cast iron bushings for a pedal block of an old VeloSolex moped for a mate.

The old ones were all wallowed out and the pedals were all over the show.

In the process of getting the pedal block off he butchered the retaining bolt and so I had another one to make too.

Perspective playing tricks with the photo there, the two are the same size honestly

Jon

Edited By Jon Gibbs on 27/06/2018 10:39:24

I would just buy medium and fine unless they come as a set of 3.

My experience is that they all eventually become "very fine" after a while but that might be the repeated use and "tongue-oil" lubrication I use

HTH

Jon

I think you were right - if you extend the thread flanks from one peak to the base of a perfect trough it is half-way i.e. H/2 down or up.

Jon

Hi John,

I'll do my best but IME you have picked the hardest thread-form to replicate first

[Edit: Legend added: A diagram of an ISO metric or Unified thread, showing dimensions relative to the pitch (P) and thread height (H). Note that while diferent standards, ISO and UTS share the same geometry, but not absolute dimensions. Also shown is the location rounding permissible in internal (dark grey, top) and external (light grey, bottom) threads. Key P: Pitch H: Thread height Dmaj: Major diameter Dmin: Minor diameter Dp: Effective pitch diameter Do not scale from this drawing.]

The best economical way to compare threads is using measuring wires (Available from Arc Euro Trade) and a micrometer. With wires you are effectively measuring part way down the flanks of the thread and so you can tell if the profiles are the same between a reference and your attempt - or indeed when using conversion tables you compare to the given effective diameter which is the diameter half way down the flanks. See the picture.

Whitworth has a rounded crest and root which can be difficult without a chaser or a die of some form. So, it is not uncommon to truncate the crests (at a smaller nominal diameter) effectively to a flat as would be the case in the metric and US 60 degree threads.

If I could recommend a new book to you. Try Martin Cleeve's "Screwcutting in the lathe". It's cheap but very good on all things related to threadcutting.

I hope this helps. Happy screwcutting! 

Jon

Edited By Jon Gibbs on 20/06/2018 08:59:19

Paul,

Ok, thanks for the clarification...and yes, I did read your posts - more than once.

Jon

Paul,

Before casting aspersions and labeling us all bad workmen did you read the posts?

Jon

Edited By Jon Gibbs on 19/06/2018 14:36:15

Hi Dave,

+1 for the comments but I think you have your left and right swapped.

Jon