Quick Change Tool Post for a small lathe.

[optima21]

its been one of those jobs that I've been meaning to do for years, but now I've finally got round to making a new tool post for my Hobbymat MD65 lathe. Here are a few pictures taken along the way. I was originally going to make one which has the tool holder clamp about a circular post, but after I started changed my mind and use an eccentric driven plunger, after having a closer look at how normal qick change tool posts work.

the main post began life as a 60mm dia x 50mm long steel bar, and its amazing how much swarf you can create from one peice of metal

then I started making tool holders from black bar, faced up using a flycutter, in my milling machine using a vice which has jaws which bolt into the T slots, so the vice can be as long as the milling machine table

then the tool holder blank needs boring out to fit the post. the cente bore of my 4 jaw chuck was a couple of mm too small, so I needed to use a faceplate on my lathe, but as I needed to bore the centre out and not damage the faceplate, I use an outer race form an old bearing to work as circular parallel and the tool holder blank is then held in place by a metal plate. and is it is being centred on centre punched mark using a spare lathe centre and dial indicator.

then milling the slot for the lathe tools in the tool holder

then I had a change of plan and decided to fit a a locking plunger in the tool post.

I ended up milling the end of some square brass on a rotary table to match the radius of the tool post, and lucky for me the post is 25mm diameter which is the same diameter as a 5mm penny washer, so one was used as a template. this hole was later bored out so the eccentric would work in it, and then turned in a 4 jaw chuck so that it would fit into a hole in the toolpost

and boring a hole in the toolpost for the plunger. I didnt have a boring bar small enough do ended up using an end mill in a boring head, which ended up working pretty well

and the completed items to assemble in the toolpost. to operate the eccentric, I decided to use a M8 cap head bolt and turned it down to 6mm, and the eccentric was later loctited it to it using a high strength retainer. the eccentric is between the plunger and cap head bolt in the picture below

and how the plunger and eccentric will work in the tool post body

and the assembled tool post

and with a tool holder, the height is adjusted using a flange head cap screw and the tool holder is locked/ released buy using the cap head bolt on the end of the tool post.the tool holder is just under 50mm x 50mmx 25mm

 

[optima21]

ohh and my old tool post next to the new one

just need to make a couple additional tool holders now

 

[DanielW]

Am I missing something? hows that a quick change toolpost?

 

[doubleboost]

Am I missing something? hows that a quick change toolpost?

The tool holder simply lifts off the centre shaft
It can rotate & is locked by the eccentric
Looks like a nice job to me

 

[optima21]

it works in the same was as this, using a eccentric operated plunger but I used a round post instead of dovetails. the cap screw on the top take less than 1/4 turn to lock/ release the tool holder

 

[rory1]

That is a fine job, I'm always amazed by the ingenuity of folk on here that make thier own tooling. Well done.

 

[711jrp]

Looks good but I think it would rotate and back the tool out, I know you are going to say it's a small lathe and only takes light cut but all the same it's not too rigid.

 

[DanielW]

Looks good but I think it would rotate and back the tool out, I know you are going to say it's a small lathe and only takes light cut but all the same it's not too rigid.

You have a point,should the tool start juddering ie parting off then it cause loosness of the post and do some right damage? these small lathes are not comfy when it come to parting off hard steels.

 

[optima21]

I hadn't thought about an issue with vibration, but it turns out it wasn't a problem, I could get the saddle assembly to vibrate using heavy interrupted cuts, but the tool post didnt budge. it also didnt move when knurling some height adjusting knobs, using a single wheel knurling tool.

the main reason why I needed a new tool post was because I needed a better quality boring bar so I could bore out some new rollers for my bead roller in this thread (which I hi-jacked a bit)

http://www.mig-welding.co.uk/forum/threads/edwards-jenny-swager.51616/

so I've now got a couple of normal tool holders for 8mm shank tools, a boring bar holder and spare holder for future use.

and at least I remembered to stamp the diameter of the height adjusting screws that I knurled onto the knurling tool shank, so I don't need to remember it next time, as its been a few years since I've done knurling as its the work of the devil getting it right.

as Im not in a production environment, its not worth the time making half a dozen extra tool holders for the time it saves in changing tools in a tool holder. one thing that is far easier that on my old tool holder, is the height adjustment, and I'll be glad to see the back of shiming up a tool to centre height

 

[711jrp]

I wasn't tasking about the eccentric as such, more the design is basically like a like a pulley on a shaft with the eccentric doing the job of the set screw, this is somewhat different to say a Dickson with the large nut in the middle, in that case the large nut clamps the square toolpost to the flat compound and it is the friction between these two flat surfaces that gives an advantage over this design. As you say... nothing wrong with cam-locks and I'm sure if you replaced the centre nut on a Dickson with one it will be fine.

 

[711jrp]

This one has the advantage of the mounting bolts holding a flat flange to the slide (unless I'm misinterpretating the pictures). Looks like 4 of them (or at least 3) so in fact a more rigid post mount than the single point style such as a Dickson.

Yep i saw that and thought it was a bit weird, as with anything a chain is only as strong as the weakest link, the toolpost is bolted on very well but the tool holder is not held onto the post too good. I was going to say something about the eccentric on the Dickson but didn't want to confooos matters. I have two Students here (don't ask why two,it's a sickness) and their toolposts can twist if you don't hoon them down when using a long boaring bar or if you run out of common sense which I can also suffer from.

 

[optima21]

yeah there are 4 mounting cap head screws on mine, and so far its not moved while being used including boring with a 3" overhang, or parting off 60mm diameter steel bar. the eccentric (cam) is 0.7mm off centre, so its a very gentle "wedge" but doesnt need much force to lock it in place, just a standard 6mm allen key.

 

[I'm getting on a bit]

The diskson tool post uses a dowel rod to stop the toolpost turning.

It is meant to be fixed with all the adjustment carried out with the tool holders

 

[711jrp]

The diskson tool post uses a dowel rod to stop the toolpost turning.

It is meant to be fixed with all the adjustment carried out with the tool holders

Both mine don't have any form of location other than the centre nut.

 

[I'm getting on a bit]

Both mine don't have any form of location other than the centre nut.

You may have a clone

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

Check out the knurled pin in this link

 

[Pete.]

Neither of mine have locating dowels either but I have had 4-ways that did. If you have a number of tool holders you can grind left, right, facing and finishing tools and have each mounted in a separate holder but if you only have a couple of regular holders in your set you're going to have to either keep swapping tools or use one tool for more than one purpose, and that usually means rotating the post.

 

[I'm getting on a bit]

but if you only have a couple of regular holders in your set you're going to have to either keep swapping tools or use one tool for more than one purpose, and that usually means rotating the post.

That really defeats the purpose of a qc. I think I have 30

But my lathe is cnc so they are essential

 

[Pete.]

It defeats one purpose, but for most non-professional users of QC toolposts the main benefit is easy adjustment of centre height.

 

[Maker]

You may have a clone

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

Check out the knurled pin in this link

Mine has a hole but is missing the pin. Does it slot into a hole in the topslide?

 

[I'm getting on a bit]

Mine has a hole but is missing the pin. Does it slot into a hole in the topslide?

You drill and ream a matching hole in the top slide (compound slide) you do this insitu

Put a tool holder on the post and use a dti to clock parallel to the crossslide the compound must be clocked 90' to the crossslide beforehand

It's gonna be 10mm or 3/8 most peeps use a length of bar with a short bend on the end (think Allen key shape) then you can use a piece of tube to wiggle it out when needs be