QCTP More rigid design

[Bgmnn1]

I am hoping to find ideas/plans to build a non dovetail qctp that is more rigid.

I am thinking along the lines of a solid pc of rectangular (square) steel bolted to the lathe cross slide with thru holes @ 90 degrees, incorporating a quick release and tool holder locators for tool position repeatability.

I have done some searching and don't find any thing along these lines.

The dove tail qctp,wedge type, does not seem to be ridgid enough when deeper boring and grooving.

Ideas, suggestions?

Thanks in advance,

Mike

[Dr Stan]

sounds like you're looking for one of these:

http://www1.mscdirect.com/cgi/NNSRIT...-SearchResults

[v860rich]

I built one that the plans were published in Home Shop Machinist, in 4 parts. It ran from Mar/April thru Sept/Oct 2002. The article is by Rudy Kouhoupt.
I think it was built for his 9" SB, I scaled mine up for use on my 16" SB. I built this in about 2005 and have used it ever since.
I change a couple things to make it quicker to use but not the origional design.
I borrowed the mag. from a friend when I made mine and my copies are kinda poor. Maybe VPress has a way to copy them for you.

THANX RICH

[darryl]

My cross slide table has two T-slots along it. I've made up some blocks that stand upright and mount to that with two vertical bolts. I bought a set of boring bars long ago that had 3/8 shanks, so I put a drill bit in the chuck and brought the carriage along, marking the center position on the block with the drill bit. Then it was taken out and drilled for the shanks. I then drilled and tapped for a bolt that could be used to hold the shanks securely- like a set screw, but I use a bolt. That's been pretty good all this while for boring, although the boring bars themselves weren't much good.

Now I have another set-up which also bolts directly to the slide using the T-slots. It holds a 1 inch diameter boring bar, and it can be set up with the cutter pretty much over the top of the slide, or with it sticking way out to the left. When adjustment range permits, I like to keep it the first way, with the cutting pressures over the slide instead of off to the side.

As needs dictate, I'll turn the 1 inch diameter down to a smaller size so it can be used in holes less than 1 inch across. The mounting bosses will remain at 1 inch though.

[Bgmnn1]

Rich

Could you post pics of your tool post?

I would like a look before hunting for the plans.

[Paul Alciatore]

You might check out my design. It was published in the Feb-Mar 2010 Machinists Workshop (V23, #1).

Here is one of the previous threads where I discussed it here.

http://bbs.homeshopmachinist.net/thr...ight=tool+post

Here is a photo of it.



The design is very sturdy because the two main pieces, the post and the holder, lock together over the complete circumference of the post and for over an inch vertically. Changing holders is fast and easy with one hand. And the repeatability is very good.

If you PM me and provide a e-mail address, I can send the latest version of the published article describing it's construction.

[J Tiers]

I am hoping to find ideas/plans to build a non dovetail qctp that is more rigid.

......................................

The dove tail qctp,wedge type, does not seem to be ridgid enough when deeper boring and grooving.

............

Mike

Why would you say that?

While I do not use that style in my shop, it is simply because I have never found that the speed and repeatability improvement would be worth it to me, and the versatility of the holders I do use is sufficient.

The dovetail (certainly the non-piston) style would appear to be as good as anything you could want. When solidly locked, it should be essentially indistinguishable from a solid piece, being "dovetailed together"...

The screw and nut serve mainly to locate, and do not have a significant support function, despite what I saw stated in a post recently. So the holder and post should be essentially the same as if they were actually made as one solid piece.

Why do you consider they are so weak and wobbly?

[JCHannum]

While it is a dedicated toolpost for round boring bars and not quick change, possibly the most rigid boring bar toolpost is the Armstrong/Williams type. It can be made directly on the lathe, as large as you wish for maximum rigidity. As it holds the boring bar on center, there is no overhang to cause flex.

http://www.ebay.com/itm/WILLIAMS-NO-...item56471e9662

I too wonder why you find the Aloris style QCTP lacking in rigidity. When boring deep holes, you can experience flex of the boring bar, resulting in a tapered bore unless a couple of spring passes are taken. That is a function of the boring bar, not the toolholder.

[ldbent]

I have a lathe that swings 18.5 inches and requires a CA/400 series tool post. A quality QCTP w/ holders costs more than I paid for the lathe. I'm going to standardize on 80 degree/triangular/negative rake/molded groove inserts(for normal to heavy cuts) and the tangential style tool holder(for finer work). I bought a half dozen brazed carbide threading tools(buck a piece on ebay). The threading tools and the insert holder have 3/4" shanks-the tangential tool holder is a 5/8" shank. I'll tape a shim to the 5/8 shank to bring it up to center height. All three tools will fit in a non adjustable square tool block. I'll have to make an adapter for the inserted cut off blade holder. $30 as compared to $900 sounds good to me.

[lakeside53]

I too wonder why you find the Aloris style QCTP lacking in rigidity. When boring deep holes, you can experience flex of the boring bar, resulting in a tapered bore unless a couple of spring passes are taken. That is a function of the boring bar, not the toolholder.

I agree.

[Bgmnn1]

Paul I have sent you a PM with contact info.

J Tiers

Think long, large boring bars mounted on very large swing horizontal lathes.


To all,

What I have is an 18" swing Chevalier. The mounted wedge type tool holders "hang" on the side of the tool post with no support directly under the tool.
OD turn tools usually do not suffer from the leverages (chatter) of the longer boring tools.
The qctp is cxa series, 1" boring bar holder.

A tool post along the lines I had mentioned originally should work well for drilling and tapping as well.

Something along the lines of the tool holders used in the Mazak T3, 1990's vintage, where the tool holders were mounted on a magazine (chain), and changed in and out of the cutting position as needed, is what I was thinking.

The Mazak tool holders had a round shank with serrations that located and held it in place for cutting.

[v860rich]

Rich

Could you post pics of your tool post?

I would like a look before hunting for the plans.

I looked for the pics but so far no luck finding them.
I think I may ahve them on a disc, I'll have to search this evening.

THANX RICH

[Paul Alciatore]

J,

When I designed my post I looked at both the piston and the other versions of the dovetail holders (as well as other designs). What I saw was that in both of these designs there had to be a lot of holes/passages inside of the post to allow the locking mechanism to work.

The piston types are the worst because they mainly grip only on the dovetails which are two narrow strips. The piston pushes the holder only at a point near the center of the back so it acts more like a pivot than a support.

The non piston types do lock a lot more solidly but as I stated above, there are significant openings inside the post and these openings will effect the stiffness.

In my design, the post is a solid piece of steel with only a central hole for the hold down stud. I could not think of any practical way of eliminating this single hole. And it is located in the center where it has a minimal effect. The holes in the dovetail styles do extend to the outside of the post where they will have a greater effect on strength and stiffness. Also, my post is entirely under compression loading before you add the stress from cutting. The hold down bolt compresses it vertically and when you clamp a holder on it, it is compressed radially. Most materials, including steel, are at their strongest in compression mode. A dovetail post has a variety of stress modes when a holder is clamped. All this makes my design stronger and stiffer. This can be important when making heavy cuts. I do admit that when cutting, the stress situation does become more complex, but that is fairly constant for any type of tool holder, even the lantern style.

The dovetail QCTPs are good. They are widely used so they are not a bad design. But I simply think that they are not the best design. I do feel that my design is close to the maximum possible for strength and for rigidity. And it does provide all the operational features that the dovetail designs do. It is actually much faster to change tool holders with my design because no tools are needed. I do it with one hand in a single motion. So by the criteria in it's name, "Quick Change" it is actually better. I do appreciate time saving features. The only feature that I sacrificed in it's design was the ability to move the tool holder to multiple, indexed positions. This is a nice feature of some posts, but it would have been hard to implement this in a home shop made post. In a way I did include a bit of this idea by having tool slots on two sides of the holders. This provides an instant 90 degree change by changing holders with tools mounted in opposite sides so I can go from turning the OD to facing instantly. For most other angles I just grind tools at different angles. Rotating the tool post is very seldom needed. Of course, the dovetail posts also have this feature.

Why would you say that?

While I do not use that style in my shop, it is simply because I have never found that the speed and repeatability improvement would be worth it to me, and the versatility of the holders I do use is sufficient.

The dovetail (certainly the non-piston) style would appear to be as good as anything you could want. When solidly locked, it should be essentially indistinguishable from a solid piece, being "dovetailed together"...

The screw and nut serve mainly to locate, and do not have a significant support function, despite what I saw stated in a post recently. So the holder and post should be essentially the same as if they were actually made as one solid piece.

Why do you consider they are so weak and wobbly?

[J Tiers]

Paul....

Not all toolposts with dovetails or the like are the sort you describe. Dickson, and others, including one designed by our own Earl of Sudspumpwater, are of the general "dovetail" type, (some inside out, though) and most don't have the "hollowing out" that you complain about.

You might also note that if you check the way forces operate in the wedge type, they act to jam the movable parts and the "solid" parts together in a way that makes them act much more as one piece.

Then again, the Aloris construction as I recall is such that the dovetail is solid at top and bottom, with a hole for the wedge in the middle, vertically. Somewhere I have the patent documents for a couple of the Sirola (the inventor's name) patents, and might look for them if sufficiently motivated.

In any case, there is a hole up the middle of the post for the worm, and the hold-down bolt. I would think it was *at least as* stable as a relatively thin vertical post ......... Although I have no doubt that your post works quite nicely. (I recall the article, I am a subscriber).

J Tiers

Think long, large boring bars mounted on very large swing horizontal lathes.

Which has ZIP to do with common toolposts and so forth........ Many large lathes don't have topslides etc.....the cutter is clamped by a large block on top of a post which might weigh several hundred kilos.

By specifically mentioning horizontal (a somewhat odd term for a normal lathe) I assume you don't mean a VTL, although it is "horizontal" relative to the normal type..... A VTL is a different animal altogether.

[kf2qd]

For deep boring and grooving the problem is generally not with the toolpost, but rather with a too small machine and the leverage the bar has on the cross slide dovetail. The dovetail block bolts down to the carriage and if the dovetail block is moving the whole carriage is moving. And when the toolholder is fastened to the toolpost, if the toolholder is moving, then the cross slide is moving. You are only going to be a rigid as the cross slide. and no toolpost is going to compensate for that...