Tool post height

Not if you leave a step at the front. You only have oreduce the underside of the tool holder for the portion that fits in the toolpost.

regards Martin

Though reducing a 12mm holder in height either way is still going to give you a more rigid tool than going down to 10 or 8mm square one

You could also mill the bottom inside edge from the toolholder, I believe they used to sell them already modified.

My advice is to ditch the QCTP and oversized shanks for the time being. Learn to use the lathe with the standard 4-way tool-post and buy a set of tools to fit it and arrange to height with shims. Keep it simple. Although 12mm tools are common, it's not difficult to find smaller sizes. Have a look at ArcEuro; although Ketan doesn't sell sets (I think), he does individual holders in 6, 8, 10, 12 and 16mm. Rather helpfully, Ketan's web site also identifies the inserts that fit the holders, removing another aggravation.

Exactly why is it necessary to fit a QTCP? Their advantage is fast tool changes and easy height setting without shims, which is particularly useful with HSS cutters. Indexed holders with pre-set shims are almost as fast, and hobbyists rarely work against the clock. I don't care if it takes a couple of minutes to shim a re-sharpened HSS cutter to height. An experienced machinist, who works rapidly with HSS has good reason for fitting a QCTP, but that's not me. Risky to buy a QTCP and shanks to fit a lathe before understanding the tool-height requirements.

Faced with this sort of problem, I think it's better to cut ones losses and go back to basics. Buy tools that fit rather than modify holders, or even worse, hack into the lathe itself.

Beginners have a lot to learn and there is no shame in making mistakes. But a good deal of trouble can be avoided by buying a few books and learning the ropes with a few simple projects before rushing to fit accessories and make changes. I recommend books rather than Internet videos because it's difficult to tell the difference between a twit who is good at making videos, and competent machinists who bumble in front of a camera. Quite a lot of fun to be had on the forum by pointing out bad-practice found on youtube.

In the absence of learning and experience problems are likely to spiral due to poor technique. I wonder how many lose interest in hobby machining due to making a false start? (I came close myself.) For example, Brian mentioned 'fixing' his problem by milling with a Jacob's chuck, which is a classic way of spoiling work. It's almost bound to end in disappointment and a misplaced rant about the quality of Chinese tools. In the early stages best to avoid tricky stuff like milling the unknown steel of a tool-holder with a floppy chuck. (Warning: lots of metals don't machine well! Don't imagine a lathe or milling machine will cut anything made of metal.)

Doesn't take long to get a feel for machining and materials. Apprentices have the advantage of starting with tools in good order, cutting metal that machines reasonably well, with an experienced mentor offering robust advice! Takes longer to teach oneself and mistakes will be made - don't rush it. Think months rather than hours. Three sources of error: machine out of order, poor choice of material, and the operator. At first, the operator is chief suspect when stuff goes wrong, especially when a novice accidentally gets into deep water.

Dave

Edited By SillyOldDuffer on 07/07/2021 09:33:48

SOD raises indirectly an interesting point in that it is my impression that QCTP's are inherently less rigid than the original 4 way tool post based on the fact it QCTP's have more interfaces between the topslide and the tool tip (one between the toolpost and the topslide and one between the toolpost and the tool holder. They generally have less clamping footprint to the topslide and quite possibly have more overhang although I haven't measured this. In order to be repeatable for tool hight they have to be absolutely clear of swarf especially when machining brass as the hight setting and clamping faces can be compromised and throw everything out. I have to admit to using a QCTP but there are occasions when I have wondered if it would be better to revert to a 4 way especially if the 4 way is in very good condition, indexes properly and has it's tools correctly set. I know industry exclusively uses QCTP's but our lathes are considerably smaller and less rigid in most cases.

I would be interested in comments.

regards Martin

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‘Less is More’

MichaelG.

I have both an original Myford 4 way tool post and a Myford QCTP set up. The QCTP gets more use because I am lazy, but the 4 way tool holder is appreciably more rigid and gets used on the more difficult jobs.

Andrew.

I entirely agree with SOD and Martin Kyte that the QCTP fitted to a typical small model engineer's lathe suffers from inherant problems, lack of rigidity due to less than perfect fits between the many introduced contact surfaces and increased cantilevered overhang from the support point below. These to reasons alone contribute to more problems than are solved by a QCTP.

Alan

I admit to *not* having used a QCTP but have always thought that an indexing four way tool post is actually *quicker*.

Which brings me to another observation that is often overlooked when the rear toolpost argument starts up periodically. Namely that rear toolposts fit directly on the cross-slide whilst normal toolposts are perched on the topslide adding at least one set of mating surfaces, more if you use a QCTP. Really, when comparing front to back the mount should be similar in order to judge how much improvement rear toolpost actually give.

regards Martin

Re the comment about inserting an End Mill into a Drill Chuck.

Fine if you are prepared to risk the cutter coming out, and ruining the work!

A drill chuck is designed to withstand axial loads, not lateral, and grips on three narrow lines.

A proper chuck for milling cutters, such as ER, 5C or Clarkson, grips the cutter shank almost all the way round, and supports the cutter against lateral loads.

Howard.

I am following the tip given my Pete above and getting a uk set of er20 collets for my DW - why didnt i think of that first - stoopid boy pike

I still have my 4 way tool post but like the way height adjustment is so easily made on a QCTP

I used a lantern tool holder on the colchester at college, what ever happened to them? They were quick and easy

also a JnS drop head holder was good but they are hard to find

I think when I get set up for milling I will skim the top of the combo slide as shown in the video

he made it easily on the ML7. I should be ok on my DW with small cuts.

Funny how you can be so focussed on a problem you dont see the obvious till you come here and a kind soul points to your mistake.

its what we do?

I hope i can make helpful contributions

You probably have already!

There may be others with similar problems, and the thread will, have given them possible solutions, and food for thought.With regard to modifying the QCTP, or the tool holder, my vote would be to mill the underside of the tool holder shanks, but not for the last 12 -15 mm at the tip end.

Removing the minimum of metal will maximise rigidity, to reduce risk of chatter, and maximise accuracy.

A tool, or job that flaps about in the breeze is unlikely to be accurate.

Howard

A real mans tool post Rocker or Lantern? Did Myford ever have one of these?

good thinking

Edited By brian jones 11 on 07/07/2021 17:19:56

The early Myford rear tool post employed the rocker principle.

AFAIK, they never offered a lantern front tool post - best left to vintage American machines.

That's what the Myford boat holders do. They were a form of quick set in not needing shims for tool hight.

regards Martin

Hi Guys,

I'm not an advocate for QCTP at all having used one and got rid of it in favour of the "Norman" patent tool post and holder. I can use 1/2" inch tools without a problem ! I don't need shims and can set tool height in a fraction of the time it takes to set a new tool using a QCTP. Particularly since I predominantly use HSS tools.

Myford also used the "Norman" patent tool post in the earlier days as did RR in their workshops. I've still got the original Myford four way but its in a box and not used any more.

I do agree about the loss of rigidity with a QCTP particularly the extra overhang that it has.

Having lowered the height of a toolholder successfully, why not make your own? Drilling and tapping for the screw is not difficult, you do need to displace the screw by about 0.003" to 0.005" to make sure the insert is pulled into the pocket when the screw is tightened.

With those all you need to do is change the base for a flat ring to give you centre height on your insert tool and you'll never have to check insert centre height ever again even if you swap from straight to left or right handed holder in the set.

The boat or rocker requires constant checking every time you move it.

If you use Armstrong holders the same applies for HSS till you sharpen them.

Sometimes the old junk is better than the new junk, depending on how much outlay you have invested in the new junk

Give me a proper 4 way toolpost every time. (These earlier things were the best that they could manage at the time )

Boat / Rocker posts don't keep the rake angle constant as centre height is maintained.

The need for greater rigidity and speed brought about the 4 way and the QCTP..

Guess what Industry uses

Their QCTPs are rigid, designed for heavy work, and quick tool changes.

Howard