A very accurate lathe quick change tool holder

[Harold Hall 1Participant @haroldhall1]

[Harold Hall 1Participant @haroldhall1]

I am in the process of adding videos to my website with the purpose of bringing to a wider audience the workshop projects that appear to be overlooked. In contact with another workshop owner very recently I commented, that whilst typically my Grinding Rest and Basic Dividing Head were being made in quite large numbers but for my QCTH I only knew of a very small number being made, he being one of them. He pointed out, something that I had not considered, that the grinding rest and dividing head appeared in my books giving them a very wide audience.

Even so, my QCTH often gets a mention on the numerous forums but is bypassed in preference to a commercial product.

Another reason why my QCTH not being taken up is that the design is often misunderstood, typically, that it uses a round post into a half round channel which it most certainly is not. For this reason, the first part of the video is devoted to explaining how the design was developed and how it works.

Another section shows how the half round channel is produced by drilling and reaming a hole on the join between two holders held back to back, being very much quicker and easier than removing a lot of metal if going down the dovetail route.

Another section, for me at least, is the most satisfying as it shows how accurate the system is. I have taken multiple measurements for both the vertical (height) and horizontal plains, taking them at 50mm from the end of the holder to exaggerate any error.

Vertically, the result was much better than 0.01mm (0.0004&rdquo with the horizontal test not being quite a good but still within 0.01mm. My contact mentioned above had also carried out tests with very similar results.

I realise that most on the forum will already have QCTH's but would appreciate it if at least some could give the video a viewing. Thanks in advance.

The Video can be accessed via my website here, click on video, top left.

Incidentally, I have 22 videos prepared but will only publish details on this forum of the few of particular interest. I have also one produced for my grinding rest showing the setups for sharpening a lathe knife tool, with the intention of creating others for endmills (both end and side), slitting saws, dovetail cutters, boring tools, drills four facet, etc.

Harold

[clivelParticipant @clivel]

Posted by Harold Hall 1 on 30/07/2016 13:32:07:

I am in the process of adding videos to my website with the purpose of bringing to a wider audience the workshop projects that appear to be overlooked. In contact with another workshop owner very recently I commented, that whilst typically my Grinding Rest and Basic Dividing Head were being made in quite large numbers but for my QCTH I only knew of a very small number being made, he being one of them. He pointed out, something that I had not considered, that the grinding rest and dividing head appeared in my books giving them a very wide audience.

An interesting video, thanks Harold, and if I didn't already own one of the Chinese wedge type QCTP clones it would be high on my list of things to make.

Which in itself is probably another reason as to why your Tool Holder is not as popular as for example your grinding rest. The Chinese QCTP clones are serviceable, reasonably cheap and easily obtainable, whereas your Grinding Rest fills a niche not (yet) serviced by the Chinese manufacturers. So given the choice of putting in the effort to make something easily obtainable or something useful and relatively unique, it is easy to see why the latter wins out.

Regards,
Clive

[AjohnwParticipant @ajohnw51620]

I took a look Harold. It's nice to see some where to point some at who wants to take large cuts on small lathes. Saves trying to explain the angles. To me it's a standard bar turning tool with increased cutting rake and clearance angle. They can be made to nearly self feed on aluminium just by steadily increasing the clearance angle.

Few people use cheque books much these days so a better term would be plastic card engineering. People are less likely to make all sort of tools even though in some cases they could obtain far better equipment than what is often offered even at pretty high prices.

John

–

[Neil LickfoldParticipant @neillickfold44316]

Thanks for the video and the posting on the holder you made. The Dickson one that I got with my Myford is very repeatable. One of the best things I did is to clean up any burs etc around the cams, and to make both cams the very same height. That way any tool can be used on either post side and get the same result.

Neil

[John McNamaraParticipant @johnmcnamara74883]

Hi Harold Hall

I really like your design.

Recently I was thinking of designing a quick change system to fit to one side of the 4 way turret fitted to my lathe. It is designed to take 25mm tool holders up to 50mm High, your holder will fit with little modification. It will increase the overhang but the top slide is quite sturdy. for seriously heavy work I can use the other 3 sides. The best of both worlds.

You can see the turret in this posting I made a while back. The 4 way tool post has accurate indexing built in, I rather like it.

**LINK**

The boring bar holder in the photo is two lengths of 25mm bright mild steel = 50mm high

Maybe the only significant change needed to fit your holder is to relocate the eccentric clamp to horizontal, to be operated from the front, the top would be obscured by the turret. I want to keep the overhang to a minimum and will have to keep it high so it does not interfere with a normal tool (25mm high) in the next station. The body of your holder can be simply clamped in a tool position.

Thank you for the detail drawings I have printed them out to add to my to do list.

Regards
John

Edited By John McNamara on 01/08/2016 14:23:44

[MuzzerParticipant @muzzer]

To me, one significant concern with this concept can be illustrated by considering the increased load on the locating feature (vertical bar feature) when the toolholder is mounted on the back face of the post rather than the side face, eg when using a boring bar.

The effective overhang of the tool cutting edge from the locating feature in the vertical direction is now increased by twice the offset distance from the centre of the toolholder – about 35mm, or an inch and a half in old money. All of the vertical load is taken by the locating feature, as a combination of torque and force, as the flat face doesn't provide any vertical support.That's quite a significant distance and it's something that most commercial QCTP systems don't suffer from as different tools are mounted. The use of multiple vees (Dickson etc) or other vertical features (Multifix) provides significant rigidity. The clamping systems in those example are also pretty beefy in comparison.

My acid test for evaluating a QCTP system would include loading the tool with a significant vertical force (some hundreds of Newtons) and measuring the deflection. That would seem to be a better test than measuring the repeatability of the positioning with a DTI without any load involved during or in between changes, no matter how impressive those figures may appear.

Murray

[Raymond AndersonParticipant @raymondanderson34407]

Believe it or not, but im with Muzzer on this one. I like the repeatability, but my biggest concern would be the fact that the toolholder is only held at one end [the front ]. Now I could well be wrong here, but would there be an area where torsion would have an effect ? Such as a heavy load wanting to twist the toolholder. I think that if the toolholder were to be located at two points ie front AND rear then that would be far stronger.

I have the facility to have the design run through FEA, If any of the engineers have a bit of time to spare. IF I can get that done, I shall put up the findings on here.

Cheers.

[John McNamaraParticipant @johnmcnamara74883]

Hi

The quick change tool post design uses a spherical mating surfaces instead of a V this simplifies the construction somewhat, the flat on the side of the cylindrical pin that mates with a bored hole reduces the effect of errors in the diameter of the pin allowing it to lock making it behave more like a V way. The flat that forms the other mating surface in the existing design ideally should be crowned, this would correct any construction errors that might cause the bearing to be only along one edge of the flat. With a crowned surface the bearing contact would be tangent to the crown radius at any small change in the angle. It could also be an embedded pin.

Mr Halls design is very compact, particularly when it is clamp mounted in a turret. As I said before there are three more tool positions available for heavy cutting. The quick change will be useful for the special form tools and high speed steel finishing tools that often require me to remove a tool to make room on the turret often for a single operation.

To reduce the overhang I plan to reduce the body of the tool to a bare minimum, the hex set screw that adjusts the height of the tool will be set point. I will remove as much of the body as possible until this set screw just clears the tool post.

Regards
John

Edited By John McNamara on 01/08/2016 17:03:00

Edited By John McNamara on 01/08/2016 17:03:49

[Harold Hall 1Participant @haroldhall1]

I cannot disagree Murray as I have always been aware of the differing situations in using the two positions. I did also consider doing a load test as well as the repeatability tests. However, having used the system for 20 years I was confident there is no actual problem.

Even so, when time permits, I will carry out some tests and include them in the video. At this point I will show my ignorance, being 65 years since I studied mechanics, and have long since forgot about the Newton, perhaps you can quantify if for me, and others, in grams.

Having come back to the thread I would say that the smiley in my post was not added by me, neither the characters &rdquo, I'm puzzled.

By accident, I have made public a video regarding my advanced dividing head. I would not normally have published it on the forum but being here it is to be found on this page.

Having said that I will only give a mention on this forum to the few that I think are of particular interest here, there will be many that will not get mentioned. I will though be emailing those in my address book with the details as each video is published. If anyone reading this would like to receive details of these go to my correspondence page and just add something to the effect of “add me to your mailing list”

Interesting idea John I have always had a liking for a four way tool post For me it is almost an "Immediate Change Tool holder", Good for batch work.

Harold

[Harold Hall 1Participant @haroldhall1]

I can understand your reservations Raymond but if you had two locating positions the space between them on the base and holder would have be spot on, and I do mean spot on. If there was the slightest error they would only mate on one side or the other. This, loosing the benefit of a large length to width ratio of the mating surfaces.

Sight should also not be lost of the ease of manufacture being a major benefit due to a lack of precision being needed.

Harold

[Neil WyattModerator @neilwyatt]

Hi Harold, 10N = 1kgf = 2.2 lbsf

Neil

[Harold Hall 1Participant @haroldhall1]

Thanks Neil but are we talking weight or torque, is that "lbs feet"

Harold

[MuzzerParticipant @muzzer]

Force is Newtons (the weight of one kilogram is 9.8N – this is what Americans would call 1kgf "kilogram force" if they were metric) and torque is Newton metres (Nm).

1Nm is about 0.74 lb-ft. 1N is about 0.22 lbf. Metric makes the units simple – no ounces, inches, pounds, stones, feet, yards, slugs, poundals, links, chains….

[MWParticipant @mw27036]

pounds per square foot/inch was a much better system, It's easy to understand how much force is involved when you imagine it. Originally, like most imperial systems it was based on real life examples. A pound/s weight applied on the leverage of 1 foot long scales.

[clivelParticipant @clivel]

Posted by Harold Hall 1 on 01/08/2016 18:28:11:

Having come back to the thread I would say that the smiley in my post was not added by me, neither the characters &rdquo, I'm puzzled.

You likely were meaning to enter (0.0004" ) however instead of the straight double quote you must have inadvertently used the closing double quote.

HTML uses special sequences of characters starting with an ampersand and ending with a semicolon to represent non-keyboard characters, for example a non-breaking-space would be represented by &nbsp ; similarly a closing or right-hand double quote is represented by &rdqo ; however the forum software most probably doesn't handles these character sequences correctly.

Smileys were originally represented by two or more characters e.g. ; ) which is supposedly a wink. Now days most software will insert a little graphical smiley in its place. Which is exactly what has happened in this case, the forum software has interpreted the semicolon from &rdqo ; and your closing parenthesis as a wink

Clive

—————-

I had to edit the posting to put spaces in the character sequences above e.g &rdqo ; because without a space before the closing semicolon it correctly displays a closing double quote. So apparently the forum software instead of parsing text from start to end, incorrectly first substitutes smiley sequences with the smiley graphic and then proceeds to parse the text.

 

Edited By clivel on 02/08/2016 00:12:06

[Harold Hall 1Participant @haroldhall1]

Thanks Clive for your explanation about the Smiley that appeared on my opening post.

Regarding the reservations relating to using the tool holder in the rear position, at this stage I am intending to test the results of taking a much larger cut than would normally be the case when using a boring tool.

To do this I will create on the end of a piece of tool steel a knife tool form but turned through 90 degrees. This can then can be traversed like a boring tool but reducing the work piece diameter like a knife tool. I will attempt a substantial cut, depth and feed rate, at the same time checking with a dial indicator if the tool bit has dropped due to the tool holder not being able to withstand the load. This I think will be more meaningful than just placing weights on the tool for the vast majority of viewers.

Will try to get this done within the next two weeks.

Harold

[Harold Hall 1Participant @haroldhall1]

I have completed the tests using my QCTH in the rear position, typically as used when boring, and have now incorporated the results into my video.

As suggested in my previous post, I produced a tool having the characteristics of a knife tool, as would be used in the side position. The workpiece was 38mm diameter and I took a cut 3mm wide hand feeding the saddle with an estimated feed rate of 0.05mm per rev, the lathe was running at 300 rpm. The cutting edge was 40mm from the toolholder. During this there was no sign of the toolholder being unhappy with the load.

Then, off camera, used power feed, increasing the feed rate up to 0.15mm per rev, again with no sign of there being a problem. However, when increasing the feed rate further it stalled the lathe as a result of the belt slipping on the smallest pulley, this being on the motor shaft. Adjusting that particular belt is not easy so I decided to take the test no further, in any case, I decided it was a worthwhile safety measure.

If you have already looked at the video you are unlikely to want to view it completely again, In this case, the tests starts at the beginning of the 4th minute

The link to the video can be found here

Harold

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Walters on 01/08/2016 20:43:08:

pounds per square foot/inch was a much better system, It's easy to understand how much force is involved when you imagine it. Originally, like most imperial systems it was based on real life examples. A pound/s weight applied on the leverage of 1 foot long scales.

But Michael, confusion abounds. Surely PSI is a measure of pressure, not force…

Dave

[duncan webster 1Participant @duncanwebster1]

Anyone who thinks that Imperial system is better than SI has not done much in the way of engineering calculations. All those odd factors af 32.2, 384, 550, 33000, 778 and so on, and even bigger heresy, using the same name for units of force and mass. I started my career using Imperial, so I can't be accused of lack of knowledge. SI is coherent and simple.

We keep on having lament about lack of young people in our hobby, then we keep on publishing designs in units that anyone under 30 simply doesn't understand. Despite what some oldsters have suggested in the past, they are not going to learn a new system of units

[Neil WyattModerator @neilwyatt]

Posted by duncan webster on 16/08/2016 18:37:37:

We keep on having lament about lack of young people in our hobby, then we keep on publishing designs in units that anyone under 30 simply doesn't understand. Despite what some oldsters have suggested in the past, they are not going to learn a new system of units

Guilty!

Call me a reactionary, but if I'm modelling an imperial prototype I want to use imperial units.

Tools, I now use metric.

If the design is to be shared it's the system I designed in or nowt.

Neil

[duncan webster 1Participant @duncanwebster1]

OK you're a reactionary!

[MuzzerParticipant @muzzer]

There was a big hoohah when the Milk Marketing Board was planning to go metric (years back!). After all, how were all the old boys supposed to learn all the new conversion factors – pints, gallons, churns(?) etc. Of course, it's very simple. One tonne is 1000 litres. One litre is 1 kg.

Michael – I have no idea why pound feet would be easier to imagine than Nm (or kgf.m is ou insist). I have no problem visualising 1kg (or 2.2lbs) on the end of a 1m long arm (or 39 inches, 3 feet 3" if you like). Given that the country went metric before you even were born and even I was taught metric at school back in the 60s, I would have expected the reverse situation?!

Murray

[DMBParticipant @dmb]

Neil,

Does your comment on 16th mean that if you received an article with drawings completely in metric dims. together with entirely metric references in the accompanying text, you would not publish it on the grounds of a likely avalanche of complaints and threats to abrogate subscriptions from the older readers?

Surely not?

John

[Author]

Posts