S&B Sabel lathe quick change tool post

[gerry45Participant @gerry45]

Hi,

I Have a Smart and Brown Sabel lathe which i rebuilt during the covid lockdown. Since then i have moved house and have have just got around to sorting the problems i found.

Dealt with the backlash on the cross feed but now need to change the tool post for a quick change type. It currently has a four sided tool post which when removed from the post has the remains of a rachet. The post that clamps the tool holder is 1inch diameter has a nut at the top to clamp it into the cross slide and a tightening handle which screws on top. What quick change tool set do i need to find / purchase that will fit the lathe? Not familiar with some terminology so please be gentle. I can take pictures of what is there at the moment with dimensions if necessary.

Thank you.

[Clive FosterParticipant @clivefoster55965]

Gerry

The official accessory quick change toolpost would almost certainly have been a Dickson type size S1 able to take up to 3/4″ shank tooling. A good quality clone should be be just fine but low end imports have a history of problems. Given the need for security and the inevitable necessity of the tool tip divining its support at significant distance a QC post is very much not the place to skimp on quality. Check the sizes before purchasing using this link.

https://www.lathes.co.uk/latheparts/page13.html

As the two parts of the T slot in the cross slide are a close match to stock bar sections the large T nut needed to hold the tool post down can be made from two sections of steel bar screwed and glued together. The nut must be at least as wide as the tool post, ideally full width of the top-slide top, if the post is to be held down properly without distorting the topside. You will also need to arrange away of locking the T-nut in position so things don’t shift when the tool post is released to rotate it. A couple of vertical grub screws running down through the nut jacking it gently up against the top of the Tee slot will work fine. Alternatively arrange a screw down locking collar on the tool post stud after the manner shown here :-

That is the stud and fabricated T-nut to fit a Dickson post on my P&W Model B lathe which uses the same style of T-slotted top slide as the Sable (and other SouthBend clones) only rather larger. The joint in the fabricated T-nut is just visible. The screw down locking collar sits nicely inside the recess in the base of the Dickson. Tightens with a pin spanner, one hole is visible. That lathe had been used for many years with a simple square plate to hold the tool post down severely distorting the area where the tool post sat. So much so that the post would no longer clamp properly securely in rotation. Took a lot of work to get things flat again, including significant building up with weld.

If funds are short consider making up several four or two way blocks similar to what you have and swopping tool loaded blocks. As you already have the remains of ratchet system it shouldn’t be too difficult to ensure things interchange and return to the same place.

Clive

[DiogenesParticipant @diogenes]

The main things you need to know to calculate the size / inform your choice of any toolpost are;

The distance from the top of the topslide to the spindle centre-line.

The dimensions of the ‘T’ nut – tho’ easy to make/modify one.

..and to a lesser extent, what size tools you need to hold.

The aftermarket ‘wedge types’ are also a reliable and solid system and usually come with a ‘T-nut’ fitting on the bottom of their post (check description/with supplier).

The holders are very cheap, widely available or easy to make, and the design is inherently forgiving of dimensional variations.

 

[Clive FosterParticipant @clivefoster55965]

Further comments concerning secure mounting.

It’s important that the post clamps down on a region close to the outer edges rather close to the centre. Obviously this gives more “leverage” against rotation when compared to holding close to the centre.

The tool post / holder mounting area of the top slide on older machines is rarely flat. Even if apparently undamaged the continually repeated stress of bolting the post / holder down tends to make the cast iron flow and rise up around the fixing. Whether the top of the T-slot or around the tapped hole provided for a mounting stud in plain topped slide. Ideally you should attend to this by machining or filing flat. If hand work is the only way and your skills aren’t up to getting it super flat a ring washer of thin aluminium does decent job of spreading the load.

The official Dickson toolpost design has a recess of diameter approaching half the width of the post to, among other reasons, shift the clamping loads away from the centre. A good idea but it does mean that a small T-nut will tend to distort the slide in the middle and not provide proper retention. Many of the affordable posts, whether wedge or Dickson clone come with rather short T-nuts. Often the centre recess is omitted too. Ive seen smaller machines, of similar size to your Sable, where the toolpost was only clamping on a ring bout 1/8″ directly wide around the post. Careful inspection showed that the apparently firmly seated post was a thou or three clear of the slide for virtually all its width. The owner complained of serious chatter. Obviously the post was rocking in the clearance under varying cutting loads. Not easy to see on the machine.

Mr Dickson uses a stepped post holding stud with a stepped space at the top to confine location forces to top and bottom. This is a more predicable layout than trying to use a snug, constant diameter stud. The top and bottom registration scheme handles any perpendicularity error between stud and slide better and ensuring well spaced, positive location at both ends where a snug, content diameter stud may only contact in the middle.

These little niceties are important to successfully coping with that gremlin infested job that is determined to chatter on you.

For me one of the nicer things about the Dickson is that they are trivially easy to disassemble to clean out any swarf that may have gotten inside. Swarf in the innards really won’t help the action of any QC tool post. I feel it’s important to have a regular maintenance routine of keeping the innards clean whatever breed you use. The innards of my Dicksons have an infuriatingly “magnetic” attraction for the really fine stuff.

And one more thing concerning use.

Whatever the breed of QC post hold the tool carrier as close to exactly in position as you can mange before locking things up. Relying on the lock to pull the carrier into place tends to give inconsistent, lower than ideal, locking forces and may damage or distort things preventing perfect operation in future. The Dickson is notorious for bending the stud carrying the height setting thimble under significantly abusive use. Maybe an annoying feature but very easily fixed and obvious evidence of encounters with gorriliod machinists in the past. Which can be important evidence when assessing a used lathe.

Clive

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