Large left hand tap

[peak4Participant @peak4]

Hello folks, I recently almost finished fettling a Herbert Junior surface grinder, and need to make some more wheel carriers, in both 32mm & 1¼".

The existing one is the normal "top hat" with a ¾" bore and a 1¼" parallel part to locate the wheel, all secured together with a left hand threaded "C spanner" collar and a large loose washer.
I thought the loose washer was just poor machining, until I realised it could be used for balancing the wheel with a bit of care.

Clearly I can cut both internal and external L/H threads in the lathe, but figured it would be easier to rough cut the internal one and finish off with a tap, so they were all the same size, and then use these to get the thread on the external parts OK as I make each one. (yes I'm being lazy).
The actual thread isn't important, other than on diameter and not too coarse.

Finding a tap at a reasonable price is the problem, and a lump of suitable steel to make one might not come cheap either, as well as the issues around heat treatment.
A 7/8" BSP Left Hand would probably do as well as a conventional 1¼" thread, but locating anything affordable seems to be an issue.

Anyone any thoughts?

Cheers

Bill

[peak4Participant @peak4]

[Tony Pratt 1Participant @tonypratt1]

You could go the other way around & make the male 'bits' first all the same size & then use them as 'gauges to finish the females, I personally would use full form inserts on the threads & check the males with thread wires.

As for heat treat I wouldn't do it but leave the carriers/arbors soft, any heat treat is likely to add some distortion to your components, your really don't want this in grinding wheel arbors.

Tony

[Brian WoodParticipant @brianwood45127]

Hello Bill,

Have you tried Tracy Tools in Dartmouth?

They are maybe your best bet for an unusual size and in left hand

http://www.tracytools.com

Regards Brian

[peak4Participant @peak4]

Posted by Tony Pratt 1 on 12/08/2020 16:41:30:

You could go the other way around & make the male 'bits' first all the same size & then use them as 'gauges to finish the females, I personally would use full form inserts on the threads & check the males with thread wires.

As for heat treat I wouldn't do it but leave the carriers/arbors soft, any heat treat is likely to add some distortion to your components, your really don't want this in grinding wheel arbors.

Tony

Tony, the comment about heat treating was intended to relate to a home made tap, rather than the wheel arbor.
I still need to make a trip over to Sheffield to collect some steel for the arbors.

Bill

[peak4Participant @peak4]

Posted by Brian Wood on 12/08/2020 16:43:38:

Hello Bill,

Have you tried Tracy Tools in Dartmouth?

They are maybe your best bet for an unusual size and in left hand

http://www.tracytools.com

Regards Brian

Cheers Brian, but the closest are some metric ones @ £85 a pop
Other suppliers are also more expensive than I can justify for a one off job, albeit of several similar components.
The difficulty is the left hand aspect, a plain old 7/8" BSP is £9, but I think I have one of those anyway.

I appreciate I could use RH threads with a locknut, but was really looking to more or less duplicate my existing arbor.

I also have a couple of wheels (that came with the grinder) with a 2" bore, but I can sort them out with two flange plates and some bolts as there is enough space around a 2" wheel bore and a ¾" spindle diameter.

Bill

Edited By peak4 on 12/08/2020 17:06:12

[Martin ConnellyParticipant @martinconnelly55370]

You can buy a 25 diameter x 100 long piece of silver steel for £14, over 25 diameter you may need to buy 330mm lengths but it will do for other jobs as well.

Martin C

[Tony Pratt 1Participant @tonypratt1]

Posted by peak4 on 12/08/2020 16:54:47:

Posted by Tony Pratt 1 on 12/08/2020 16:41:30:

Tony, the comment about heat treating was intended to relate to a home made tap, rather than the wheel arbor.
I still need to make a trip over to Sheffield to collect some steel for the arbors.

Bill

Yes I just re-read your post,I must be getting old

Tony

[peak4Participant @peak4]

Posted by Tony Pratt 1 on 12/08/2020 18:31:18:

Yes I just re-read your post,I must be getting old

Tony

Don't worry, I know I am.
Just taken my glasses off to type this.

Bill

[Martin ThomsonParticipant @martinthomson36607]

Posted by Martin Connelly on 12/08/2020 18:11:20:

You can buy a 25 diameter x 100 long piece of silver steel for £14, over 25 diameter you may need to buy 330mm lengths but it will do for other jobs as well.

I don't know where you're buying your silver steel from, but that price is ridiculous. 333mm of 25mm silver steel is £11.99 from zoro. A bit that's big enough to make several 1.25" taps would be £20.

However, only a crazy person would try and cut a thread over an inch with a carbon steel tap. Even a HSS tap would be hard work. A homemade tap of that size is unlikely to do anything other than break part way into the nut.

Just cut the threads properly on the lathe. Left hand threading is away from the chuck so it so easy even a total beginner could do it. And for £20 you can buy a big lump of hex stock to practice on.

[Oily RagParticipant @oilyrag]

I must admit I am at a bit of a loss as to what you are actually threading, are you referring to threading the wheel carriers? If so why? surely the wheel carrier will sit on the plain portion of the spindle and then the wheel will be clamped with a LH nut pulling up to a suitable washer which covers the wheel – not forgetting the paper washer interposed between washer and grinding wheel.

Most English grinder spindles used either 1/2" or 5/8" BSF LH threads in these small size machines (Herbert, Eagle, Dronsfield along with Clarkson T&C cutter grinders) – Tracy are advertising 1/2" LH BSF for £15 – good value for money in my estimation.

[Tim StevensParticipant @timstevens64731]

Martin Thomson repeats a factor that seems to me to need explanation – that HSS tools cut easier than carbon steel. My understanding is that HSS will hold its edge at higher temperatures than CS, so it is preferred in workshop use (and has been for over 100years) – but what is it about HSS that improves its ability to cut? I just wonder, for example, whether anyone ever made HSS razors, and if so were they better? I mean real razors, not blades.

Tim

[Clive Brown 1Participant @clivebrown1]

My long-held belief, not supported by much evidence I must admit, is based on commercial CS taps generally being cut threads whereas HSS taps are ground threads. The grinding process allows for better clearance and rake angles, improved finish and sharper cutting edge in the "as-new" condition.

My tuppence worth!

[Keith LongParticipant @keithlong89920]

Bill – I'm looking at designing some grinding wheels hubs myself at the moment ,and I'm using the William Sopko catalogue (or catalog as it's an Americam firm) for inspiration. They list some hubs suitable for reversing applications. Their method is to thread the wheel retaining collar either right or left hand according, presumably, to it's normal running direction, but them they drill and tap radially into the edge of the retaining collar and fit a couple of nylon tipped grub screws. They can be nipped up to lock the retaining collar against unscrewing in "reverse" rotation. For routine "reverse" running you might want to fit more grub screws as "belt and braces", but it could mean that you can use a normal RH tap at a much more sensible cost than the LH version. If you follow this link it will take you to the Sopko website and the reversible hubs.

webpage http://www.wmsopko.com/sopko_04_22_28_30_44_50.htm

Keith

[peak4Participant @peak4]

Sorry folks, I thought I'd been clear enough in my initial description, but the problem is the same as always without a proper proofreader.
I can visualise what I was saying, I've got the parts to which I was referring as well as a mental picture, but it's obviously not clear the way I worded the question(s)

Firstly, I've never suggested tapping anything from scratch, merely cleaning up a roughed out thread(s) I'd already cut in the lathe, to make sure it's not "drunken"; I'm quite happy cutting left hand internal threads, though it's not something I've had the need to do very often.

Oily, or Mr Rag if you prefer, on my Clarkson, as you say, there is a left hand ½" BSF thread, which you use with appropriate spacers etc to fix the wheel, exactly in the manner you describe.
I've actually made several extended carriers, duplicating the main spindle, so I can have several different wheels ready mounted.
The little Herbert surface grinder works slightly differently; probably more akin to other surface grinders, and the wheel is held in a demountable carrier.
It's only got a 6" wheel capacity, and the normal bore size seems to be either 1¼" or 32mm, depending on the wheel material and source. Unfortunately, some vendors seem to think the two sizes are interchangeable, and don't always supply what's expected/advertised.

Keith, many thanks for your link, most useful.

My intention is to make a number of carriers, so I don't have to re-balance the wheel/carrier combination every time I change wheels. There will be more than one design, but for the time being I'll more or less duplicate the one which came with the machine in both 1¼" and 32mm.

Here's the disassembled wheel carrier;
Left to Right; wheel carrier/rear flange – front flange – securing ring/nut

Assembly order;
The "Top Hat" on the left has a parallel section 1¼" to suit the bore of the wheel, the front flange/washer is keyed, and also has a different depth recess each side to accommodate either ½" or ¾" wheels.
The washer/flange is actually a very loose fit on the bore size; I don't know if it's original, intentional, or just poor engineering.
That said, I've found that by offsetting it slightly from central, I can use it for balancing the wheel; this design of carrier doesn't allow any other obvious method, and I'm not experienced enough, or comfortable doing it the old way with a masonry bit.
The right hand item holds everything together. I've actually made a spacer so I can use a ¼" thick wheel as well.
The thread twixt left and right parts is undersize from 1¼" and actually measures at 1.22" @ 22tpi
This is the left hand thread I'll be cutting on both parts, as many times as the number of carriers of this style that I make.
The only reason for a tap was to smarten up and standardise the ID of the thread internal to the ring nut, so it's hardly essential, just time saving.

The rear of the top hat carrier also has a concentric ring cut into it, to act as a very basic labyrinth dust shield for the main spindle.
It has a through bore to suit the ¾" main spindle

The parts assembled ready to fit to the spindle;

As you can see, the main spindle has a step at the end, and the assembled carrier/wheel is retained by a single ½" L/H BSW nut and plain washer. (annoying as I already have a L/H BSF tap from when I made the Clarkson adaptors)
You can also see the triangular annular ridge which forms the other half of the dust excluder, this is on a static part, and doesn't rotate with the spindle.

Cheers Bill

Edited By peak4 on 13/08/2020 21:19:04

[peak4Participant @peak4]

Split post as the previous was too long.

I also have a couple of wheels with a 2" bore, which will allow me to use a simpler design of two parts held together with a ring of bolts, as there should be space within the 2" bore to accommodate them.
These are actually 1" thick, which is oversize for this machine really, but it also means that they won't fit the existing holder, even with a bore spacer.
Similarly I have a couple of diamond wheels, with 32mm bore, which are obviously solid aluminium, so I can knock up a permanent adaptor for each. I've got a large lump of alloy in stock somewhere.

Hope this clears up the various queries;
I'll probably just do it all the normal way on the lathe, but thought someone might know of a source of L/H 7/8" BSP taps, or similar alternative but with a finer thread ideally, which would come in just undersize for the 1¼" as per existing, albeit with a coarser thread. Certainly isn't worth me shelling out £85 for a convenience factor, or even £30-£40 for a lump of silver steel, the rest of which I'd likely never use.

Bill

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