Cross-slide fixture plate considerations

[CalumParticipant @calumgalleitch87969]

So this turned up during the week – very well packaged from M-Machine. I took John's advice and went for steel in the end. They were out of stock of 1"x5" or 120x25mm, so I took a piece of 360mm x 3/4"x5" which fits well with just a couple of mm overhang on the sides of my cross-slide. I'll use 6 M8 cap screws to mount it.

I took my lathe to bits (again) and started plotting out where to put the screws. The thinner shell at the back is still about 12mm, so I think plenty for a 1.25 pitch thread to hold onto. At the other end, those of you who have this lathe or something similar will spot the deliberate mistake…

I spotted it as well, but not until after I'd congratulated myself for avoiding the opportunity to drill through the gib:

The problem of course is that the circular T-slot will be fouled by the location of that screw on the left. However, as I was yet to realise this, I went ahead and punched for the drill:

You can just see the circular slot through the smaller hole on the left of the large compound locating hole. I turned the slide over to check, and said some very un-ladylike words. Some gentle attention from a Dremel and a grinding bit removed the burr from the punch, and I moved the hole somewhere more sensible.

And so over to the drill press. I could have just about got it in the vice but it seemed more trouble than it was worth. I have to admit I'm not a fan of this table – I'd prefer a piece of plate with through holes/slots. This thing gathers clart and small tools like no-one's business and the T-slots are fiddly (and the top section too thin – I've broken a chunk out already). I often find myself just clamping stuff down with the G-clamp.

Six holes of swarf later:

Then transfer punch the holes to the steel plate:

And drill out the steel plate for M8 thread clearance:

I hadn't thought about the fact the socket heads are 13mm in diameter, and I don't have a suitable clearance drill. I tried counterboring one hole with a 13mm drill, in the hope runout might win the day, but no. At this point I also realised (a) I had forgotten to drill clearance holes for the compound T-nuts (T-bolts?) , so did that, and (b) that although 3/4" thick steel is nice chunky stuff, it's still not enough to properly clear the bolts! I don't think it'll be a major problem, and if in the end I have to remake it in 25mm stock, well.

A 13.5mm drill to counterbore is in the post, as is (still) a set of M8 taps, so we're not quite done, but we're well on the way now.

[Bill PhinnParticipant @billphinn90025]

Is there a reason, Calum, why you don't want to use a counterbore bit to counterbore your holes?

[CalumParticipant @calumgalleitch87969]

Bill, I have to confess ignorance! I didn't know such things existed, though it makes sense that they do.

I think for my purposes a caphead will seat happily on the cone left behind by a drill – I don't doubt my counterbores aren't perfectly in line with the screw in the cross-slide but it should be pretty close.

Having a quick look at available counterbore bits the counterbore size seems a bit large – to my mind a 13mm cap in a 15mm counterbore will look a bit spacious, and the pilot hole size seems to vary!

[Bill PhinnParticipant @billphinn90025]

Hi Calum, attached are pictures of some counterbores I did, in:

M8 aluminium

M5 brass

M3 mild steel.

My pilot and cutter diameters are respectively:

8.2mm/13.4mm

5.2mm/8.9mm

3.2mm/5.9mm

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