ShopTask 1720 XMTC Multifix Toolpost

Description

This is a sub-project of https://hackaday.io/project/169581-reviving-a-shoptask-1720-xmtc-gold-3-in-1 in which I replace the original lathe toolpost with a Multifix 'A' Quick Change Toolpost. I chose this style of QCTP rather than the Aloris type more common in the US as it seems to me to be a better design, and more suited to a machine which will be getting CNC capabilities in the future.

Details

The original toolpost is a turret type, 75mm on a side with a fixed height set to bring a 12mm lathe tool to the spindle center which is 100mm above the table. The turret sits on a roughly 75mm cubic chunk of cast iron which has a 30mm hole through it and close fitting t-slot keys. A 30mm rod with an integrated T-nut holds it to the table when tightened by a 12mm threaded rod with a handle on the top. As far as turret toolposts go, it works pretty well.

A while after purchasing the machine I bought the Shoptask QCTP, which turned out to be proprietary - and poor - design. This toolpost was only offered for a short period and later vanished from the Shoptask website - presumably from embarrassment. While the toolpost itself is effectively junk, it sits on an almost identical cast iron block, complete with t-slot keys. The plan is to recycle this item to support the Multifix. Initial calculations show it to be pretty near the ideal size and height. This will leave the original post intact to keep the machine functional should I upgrade to a dedicated lathe in future and move the Multifix to that.

The toolpost is on order from pewetools.de and will hopefully be here by Christmas. I have some 12L14 for a new hold-down in the mail from hobbymetalkits.com which may get here by the weekend.

Project Logs

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Delivered and Installed
Alastair Young • 01/26/2021 at 02:48 • 0 comments
With the 25 day back-order and 4 weeks shipping time, it finally arrived last Friday. So now it's installed.

I initially was looking at Create Tool as I am cheap and could have had 2 or 3 more holders for the same price. They never responded to emails, so I purchased from pewetools.de . Their website was up to date, but the parts I was after ( the AD1675 kit) was listed with a 25 day delay. After I ordered they followed up to confirm this info and followed up again when the item shipped - and again after it was in transit. Clearly they provide good customer support. The parts appear to be excellent quality also - and very well packed.

All present and correct.

Support faced down 5.3mm so A20XX tools and the cutoff tool will be low enough, and 12mm tools can be raised high enough. That's an 8mm range and the size A post has an 11mm travel - so this height is pretty specif. Final height of the base is approx 70mm.

Post nearly done. The two steps are 26mm and 20mm to be a slip fit on both internal diameters of the toolpost. As before, the final dimension is snuck up to with emery paper.

Install completed with stainless steel 1/2-13 UNC nut. That's what ACE hardware stock. I could have gone 12mm but the 1/2" is just bigger and beefier. I turned the serrations of the bottom of the nut and lapped it smooth.

Squaring it up before installing the dowel pin hole.

The post sets a 12mm (or 1/2") tool about 0.9" closer to the chuck, which somewhat offsets the lost travel on larger work from the DRO scale, so I'm less worried about banging into it with the 4-jaw chuck. I really want a smaller 4 jaw chuck - the 6" is really too big.

All that's left to do is:
- to figure out a way to zero the DRO accurately when swapping the post back in. I have an idea that uses an electronic edge finder.
- grind the tip of the parting tool blade. The 20mm x 2mm blade has dovetail edges to fit in the holder so the tip, although it has relief, has an angle where it would cut.
Post bottom half
Alastair Young • 12/12/2020 at 08:06 • 0 comments

I have replicated the profile of the old t-nut onto a 180mm chunk of 1-1/4" 12L14 round bar. Final dimension was snuck up to with 600 grit wet and dry, so it is a closer fit in the block than the original. Turned between centers.
Nothing more to do till the toolpost arrives.