How to size up a quick change tool post

[dawesy]

I'd like to get a quick change tool post for my Churchill lathe but as its a rare one I need to know what measurements I need to get the right qctp.
Has anyone got any tips?
The current one is about 3" square with a 22mm or so groove round for the tool bits.
Any help gratefully received.

[awemawson]

Well stating the obvious it needs to be able to present the tool tip on centre height and be able to accept the size of tools that you use. I suggest that a good starting point is to measure from the top of the top slide (ie where the tool post mounts) to centre height. Then select a post that puts its tool tip such that the height adjustment straddles centre height.

[chipenter]

As yours is a 6" lathe go for Harrison / Colchester size , you could reduce the height if necessary , the chinees push piston type are the easiest to make holders for , but Dicenson Bison are the best but you do need deep pockets .

[Joules]

If you got a Myford style Dickson toolpost cheap, you can always add packing below it to raise the centre height if needed.  As stated, what size tools do you generally use ? Do you use the full 22mm or smaller.

[Pete W.]

If you go here:

http://www.mscdirect.co.uk/CGI/INPDFF?PMCTLG=00&PMPAGE=675&PMITEM=TQC-79020M

There's a useful table of dimensions for the standard sizes of Dickson style Quick Change tool-posts.  You might have to wait a few seconds for the page to open!

Usual disclaimer - no connection other than as an occasional satisfied customer. 

[Jonny]

Looks like a T2 or T2T which I had as original issue on M300 and found on the small flimsy side plus didn't like cost of the tool holders.

Changed for the Chinese piston 250/200 Series I had on an old Harrison 140, have 4 still got an unused one spare no holders. Can open up holders and centre some tools 26mm tall and work out £96 for 5 Vees (250/203?) delivered from Gloster. Not as good as the Dickson for repetition alignment but ok for most work, I wouldn't have bought 23 holders and needing think its 12 more.
If do go this route you may have to purchase holders from same place, many I have bought from numerous other places ie Allendale and two more they call by a different number. No argument if you specify 250/200 Series you know they will fit.

The reason for the 7/8" slots is to allow packing under chosen tools.

[dawesy]

Thanks for the help and advice guys.
One thing I forgot to mention is the current tool post has a 2  1/2" circular boss that it sits and spins on ( I'll get some pictures to show this) would this have any effect on tool post choice? Or would it need milling down to give a flat top to the compound slide top?

[Jonny]

Post a picky up.

Whether top slide or tool post is cylindrical wouldn't matter as long as flat. Probably will have to change the thread for tightening up, worst case mod the base to a T slot.
Modified my M300 to same fitting as Harrison 140 that does have a T slot. That way can just slacken off 1/4 rev and pull whole toolpost out and load another in. Downside Is no 90 degree indexing. The piston type Chinese QR toolposts come with this T fitting.

[chipenter]

You will need the height from the top of the boss to centre pluss about two thirds of a tool holder , will alow you to use tools the maximum of the holder groove.

[dawesy]

Ok so  I've took a couple of photos.

That's the raised boss I was talking about.  The two sunken cap heads you can see attack to the lead screw nut.

That is the distance from the top of the compound slide to the top of the tool bit. The tool but is in centre hight.

[chipenter]

I intend to buy a Boxford T1 quick change tool post from RDG at Sandhust Park Exibition , but I want to look at it first there is just not enugh information on the web site , I could let you know the sizes if you can waight that long .

[dawesy]

That would be great. I'm not in a great rush

[chipenter]

OK it's in two weeks.

[stig]

I run a Harrison L5 which is a 9" lathe (4.5" to centre). I found the T0) tool posts suitable for the myford would have achieved the right centre height that I needed but the main holder was too small a square section that the attachments didnt clear the cross slide far enough to allow the tooling to carry out its duty where needed (not enough overhang)
I therefore went for the T1 which achieves the same height and will just about accommodate 16mm shank tooling and at the same time align on centre whn the holders are at the bottom of the slide

hope this helps

[dawesy]

Thanks for the info.
I'll have a measure when I've finished rearranging the workshop.

[chipenter]

As RDG where out of stock I bought one from Chronos Boxford size made by Soba , the tool holders are 73x32x30 and take 16mm tools , the heighest the holder will go is 25.5mm from the base to the bottom of the tool , on my lathe a 1\4" tool leaves a small pip , the largest that the base can be bored out to fit your boss is 1 1\2" , hope this helps .

[dawesy]

Thanks for the info. I'll have a measure when I get 5.
Only problem if have is I do have some 20mm tools as well.