QCTP

[Chuck in E. TN]

Having recovered from a bout of "I hate my job" type depression and malaise, I've decided to gather plans for making a QCTP. I learned a lot making dovetails for Harold Hall's precision grinding table which is almost finished.
I started with a Google Search for QCTP plans and have found several. In one design posted by John Stevenson, he references BDMS, which I asume is a type of mild steel. Can someone translate to "American"?
As I gather more designs to ponder, I will post more questions here. I already have made a  few toolholders of the Norman Patent style as touted by Mert and Ralph on the yahoo 7x12 site, and I like them. I may just re-work/refine those, as my skills have greatly improved since making them.
The Noman style aside, what is the concensus of opinion on wedge vs piston type?

Chuck in E. TN

[John Rudd]

In one design posted by John Stevenson, he references BDMS, which I asume is a type of mild steel. Can someone translate to "American"?


Chuck in E. TN

Chuck,

Bright Drawn Mild Steel...........

[rleete]

Bright drawn mild steel is commonly known as cold rolled here in the US.  Any low carbon steel will do.

[Country Bubba]

Chuck,
I will jump into the pool on the discussion of piston vs wedge.
Bottom line from what I have read is either will work fine for most of our type of work. But having said that, I went for the wedge type on my 12" as I feel the tool holder is better supported by wedging the entire length of the dovetail (and it is also pulling it into the post) whereas the piston type is pushing on the toolholder.  Depending on the height setup, it is my opinion the piston might not be centered on the holder and possibly loose some of its effectiveness?

Art
Country Bubba

[buffalow bill]

Chuck,
Just to trow my 2 pennath in, have you seen Harold Halls solution,  http://homews.co.uk/page38.html . Link to his web site.
Have been looking for a sinilar solution, but now the workshop has been put into storage. Will be glad to see your solution.


Bill

[Jonny]

Had a quick look at that Bill, looks the worst of the lot.
Hate to think what the rigidity is like and also the repetition when changing over.

The Dickson style of toolpost is far the best, support against the tool post. Unfortunately i gave a large one away and now only a T02 a bit on small side with 1 tool holder.

I normally use for convenience the chinese dovetail and will have to change. I have noticed for weeks trying repetitive stuff swapping and changing tool holders over, i cant maintain dimensions. The reason the toolposts are flexing, if its pushing against one dovetail, its got less grab on the rear in the case of boring, therefore comes out undersize.
You can physically see the toolpost veer off when knurling.

[AdeV]

I built a piston type (http://madmodder.net/index.php?topic=3453.0), and in practice I find it works very well. It helps to have the toolholders to be a fairly tight sliding fit over the dovetails, otherwise it's possible to end up with the piston acting as a fulcrum allowing the tool to rock in the horizontal axis - not fatal, but you need to be aware of it, and of how the cutting forces are going to affect it, and make apprpropriate allowances. On the other hand, get a nice snug fit and there's no noticable movement when you operate the cam.

If I were to make another one, I'd probably have a go at a wedge type, although I do have most of the bits for another piston type...

[jgroom]

Hi Chuck.  

I built one of Mr. Stevensons' toolposts several years ago.  It was a bit huge at 3" square for my little 9"SB so I dropped it to 2.5" square.

It still feels a little large, but it's extremely stable.

I built a smaller one I found in Home Shop Machinist (can't remember the issue date) to get in a little closer to the chuck.


Both work very well.

Any Loftquist has a very nice looking compact toolpost, http://www.statecollegecentral.com/metallathe/MLA-23.html.  The drawings for it have also appeared in HSM (May-June 2006).  May have to build one for the fun of it.  

I've never used an Aloris style piston type post so I guess I'm no help on that front, but I've never had a problem with the wedge type.

Cheers

Jeff

[BillTodd]

I made this Hardinge style one for my HLV_H. Inspired by this design on the HMEM site:

http://www.homemodelenginemachinist.com/index.php?topic=5153.0


Bill

[Chuck in E. TN]

Thanks for the input so far. I have collected a couple of plans and pasted them into a word document to study further. I still lean to remaking the Mert B./ Ralph P./Norman Patent variety. The first one I made was from 6061 aluminum block on a steel cylinder. I cut the clamp slot with a hand hack saw, but that was before I had a 4x6 band saw and some decent slitting saws.
Any other ideas floating out there?
One more question. The standard 4 way Chinese tool post, any clever mods to make it more useable, like adding height adjustment?

Chuck in E. TN

[andyf]

Hi Chuck,

If you are going for the Norman Patent type, you might consider this one http://mikesworkshop.weebly.com/novel-quick-change-tool-post.html which takes two tools in each holder block, with independent height adjusters for each tool.

I doubt if a standard "4-way" type could be easily adapted so as to vary its height. You need a thick (around 1") post for it to clamp on to securely, and there isn't enough metal in between the four tool slots for a correspondingly big hole.

Andy

[bp]

A while ago I made a pillar and clamp-on toolholder style QCTP.  One of the reasons was to eliminate the tool overhang from the top slide and as a result increase rigidity, and provide better parting off.  These requirements have been met. 

Anyway I wouldn't use aluminium alloy for the toolholder, it simply isn't rigid enough although others will no doubt disagree.  Also I made "my" pillar as large as possible to increase clamping area and to increase the seating area onto the compound slide.  The pillar ended up at about 35mm diameter.  My toolholder used 12L14 (free machining) steel 35mm nominal diameter for the pillar, and 25mm slices off of 50mm x 50mm bar for the toolholders (all 14 of them)
cheers
Bill Pudney

[Metalman]

I wonder Jonny if you have misunderstood Harold Hall's QCTP. It is easy to look at the photographs on his website and think that it is a half round key locating in a half round groove, which of course it is not.

The inner member has in fact a flat on the top so that the outer just locates on the sides rather like a mini inverted dovetail assembly and should locate very well.

Another very important consideration that he mentions on his web site is that the location has a much greater length to width ratio than other designs, that he comments are about 1:1. I estimate the difference to be in the order of 4:1 for his design compared to the 1:1 that he mentions for other designs.

The main consideration for the design, published in MEW issue 50, is that it is quick to make and at a push can be made in the workshop that does not posses a milling machine.

Kenneth

[Jonny]

Ken, what happens when one material is softer than the other and or when it starts to wear. That will be the first time its used.
Even if both parts are same metal one will wear the other rapido.
Looks slow to change as well as tolerances have to be tight making alignment and fitting a chore. Will egt better over time with wear.
In saying that should be better than any dovetail push out type.

Wedge type pull in as in Dickson far the strongest.

[Doc]

Here is a set of drawings for the one I put together and built for my lathe.

[BillTodd]

Here is a set of drawings for the one I put together and built for my lathe.

That looks like the one I copied      

Works a treat