"another" toolpost question

So...
Would you rather have a toolpost a little on the small side or little on the large side.
Most every spec and recommendation for my lathe is a CXA.

This lathe.

https://acramachinery.com/product/1660tvs-precision-variable-speed-gap-bed-engine-lathe/

But a BXA should also work. The lathe is not a heavy duty unit and the machining I do is relatively light.
I would prefer to get a BXA as it is quite a bit cheaper overall.

What do you think? Go for the BXA?

Thanks

Glen

Dunno, you could go either way on that one. I think its best to have the tool post covering as much of the slot as possible, just for strength. I used a Acra 1440TE for a while and it had a BXA that was just about perfect for that machine. But your machine is probably a bit bigger than that. So I wouldn't be afraid to use the CXA except for the price....

Check the base thickness of the tool carrier before deciding to go bigger than the BXA.

Theoretically a larger toolpost lets you use larger shank tools but the bigger toolholders tend to have thicker bases which limits the size of tooling that can be bought to centre height. Its quite possible for things to pretty much cancel out with the thicker base lifting the tool so far that next size up shanks won't work. Particularly important when using carbide inserts with standard sizes of shank and fixed tool heights. life is too short to machine downa bunch of larger tooling so it fits.

If you are doing light machining is a larger shank capability of any benefit in the real world?

Another issue with bigger toolposts is that they are all round bigger, take up more space and get in the way more. I find this can be a right pain when using a tailstock centre as the tailstock barrel sometimes need to be near full extension so the post doesn't argue with the tailstock casting.

Its a pity no one makes a system using quickly interchangeable block posts, either two (better) or four way. Carbide holders don't need shimming anyway and ground HSS is easy to do off the machine with a very simple jig. Simpler, smaller, cheaper. Only needs some form of quick release nut and positive location for the base. I got as far as concepts.

Clive

what sometimes happens if the toolpost is too small (toolholder too short) is that the tool has problems reaching the work beyond the compound.

in my experience, the extra mass of a larger tp is beneficial . also, i buy my carbide and toolholders at
surplus- and 1" shanks typically sell for much less than 3/4 . i run the square 5.5x5.5 that holds up to 1.25"
shanks. i know most people hate them, but i rarely change the four tools - and if i do- all my replacements
have been pre-shimmed to center and slip right in with little fuss. fully loaded , it is a lot of mass-
probably 25 lbs or so.

Clive603 said:

Its a pity no one makes a system using quickly interchangeable block posts, either two (better) or four way. Carbide holders don't need shimming anyway and ground HSS is easy to do off the machine with a very simple jig. Simpler, smaller, cheaper. Only needs some form of quick release nut and positive location for the base. I got as far as concepts.

Clive

Click to expand...

Both Aloris and Dorian make a quad toolpost for their style holders. Google CAI for Aloris or QITP for Dorian. Sit down before you look at the price though. And having used one, I'm not really a fan. They use a little funky tool to change the holders, the large lever on top is for rotating the 4-way. If you use even a single tool like a boring bar, the bar blocks the use of any other tool in the slot immediately counterclockwise from it, essentially making the 4-way a 2-way unless you are using a very short part that doesn't require the tailstock at all. I much prefer the regular Aloris.

Aloris and Dorian have to be joking (laughing all the way to the bank).

Misses the point in so many ways I can't believe they'd try to market them. Standard Dickson QC sets, like mine, have holder mounts on three sides which is handy although I've only used the tailstock side one a handful of times, really needed it tho' as the alternative would have been breaking out the lantern. But nobody seriously suggests you should rotate the post to change tools. Mine live square to the bed axes. More likely to rotate the compound than the post as there is a nice scale to put it back.

As you don't have to adjust the height of carbide insert shanks a simple block style carrier is perfectly acceptable provided you can release them with the usual QC style 1/3 rd of a turn or so on the hold down. They can be lifted off and swopped just like a conventional QC.

My concept sketch had the business end of the holding stud provided with a cross drilled hole for a tommy bar and arranged to rotate. Tool block was to have a threaded sleeve with a castellated end sized to match the tommy bar screwed into the top. Basic adjustment of the sleeve would lightly hold the tommy bar in the stud via the through hole when passed between the castellations. Tighten up a bit and everything would hold securely, loosen a bit and the tommy bar could easily be pulled out. 1/3 rd of a turn between tight and loose sounds about right. Need an index pin or face splined plate underneath for location.

Plenty of other ways to achieve similar, especially on a production line, such as interrupted thread, locking bayonets or rotary weding things as on conventional QC systems. But my idea seemed very appropriate for shop made.

Clive

Cxa on my 12” Hendey I could see being I little short on a 16”. Do like the size of em they hold a decent size tool without having to mill them down and aren’t to heavy and bulky and a block under could correct that.

Besides greater ridity of larger posts, each consecutive size up allows the #1 toolholder for respective sizes to go up by a size. Example, CA1 can hold 1" tools, CXA1 holds 3/4 tooling, BXA 5/8 or 1/2" etc.

Also the posts get shorter as you go smaller. Might need to space the post up to hit centerline.

If you go to Aloris site and search a post and also its #1 holder you can see dimensions. Measure top of compound rest to work centerline, might give you a better idea.

They make #1 holders for the next largest shank size as well. For example CXA-1 is 3/4. They also offer a CXA-1XL for 1” shank.

slodat said:

They make #1 holders for the next largest shank size as well. For example CXA-1 is 3/4. They also offer a CXA-1XL for 1” shank.

Click to expand...

That is true, but is also the reason I went with CA on my 14×40. 1" shank tooling is everywhere and frequently at very cheap price. And I never see a CXA-XL on eBuy. I can also stick the tool way out if necessary with no rigidity worries.

Larger or smaller? Why not one that is specifically scaled for your lathe?

Why not one that gives you THE fastest tool holder change?

Why not one that provides the ultimate rigidity?



Rock solid stability: the post is solid steel with only a central hole for the mounting stud.
And the tool holders wrap around the post with a very large area of contact: the post and tool holder are like one, solid piece of steel. The central stud places the post in compression for extra stability.

Excellent repeatability: There is a large flat on the post and a height adjustment screw that provide repeat positioning that is well better than 0.001" in all three axis.

Fast, One Hand Tool Change: This design offers a very fast tool change. A tool holder can be removed with ONE hand, NO TOOLS, and using ONE continuous motion. The installation of the new tool holder is equally fast and easy, again with no tools and ONE continuous motion. Quick tool changes are the essential idea behind a QCTP and this design offers the fastest possible tool change.

Independent Adjustments: Tool height, angle, position, all adjustments are independent of each other to the maximum extent possible.

No Dovetail: The dovetail of many tool posts offers a very small area of contact between the post and the tool holder. This can have negative effects on the positional accuracy, repeatability, and rigidity. And it is harder to make. This design offers an easy to machine, round post with a generous flat for accurate positioning and rock solid rigidity.

Self Cleaning: There is virtually no place for chips or other debris to hide. The action of installing a tool holder wipes the mating surfaces clean. And if you insist on cleaning them, those surfaces are readily accessible so cleaning is a matter of a fast wipe. There are no hard to reach corners.

Easily Scaleable: The drawings are scaled for a SB-9 but can be easily scaled up or down for almost any size lathe.

Here are several ways to obtain the article with photos and drawings:

Original Article:
Quick-change Tool Post, Feb-Mar 2010 Machinist's Workshop
Back Issues << Machinist's Workshop << Metalworking << Storefront << Village Press

Free Download of later version:
Dropbox - QCToolPostRc.doc - Simplify your life

Latest version:
Quick Change Tool Post for Lathe - HomemadeTools.net