Member postings for Dr_GMJN

Still struggling a bit with the straps - a bit of fettling needed tonight, but I think I’m getting there.

The casting flaw I didn’t pay much attention to: it turns out only about 0.3mm needs machining from the o/d, even roughly measuring a Blue-Tack positive impression showed it would definitely still leave a hole:



As suggested, I milled a 3mm hole, but went straight through the flaw and into the I/d. Then turned some similar material (from the spare bearing block) to be a tight fit, then tinned with solder, tapped into position and sweated in place. I misjudged the proximity of the hole to the edge (it now has a very thin wall), but in the end it held:



After filing back, I think it will be fine once finally machined:

I wonder if the left-hand turning tool with the diamond insert gives 45 degrees for chamfering when set perpendicular to the bed?

I'm not at home at the moment, but that might be an option, albeit making the tool holder more likely to hit the chuck at small workpiece projections.

Yes, I often do the same, but for getting things consistent (e.g. the small chamfers on the P.R. eccentric fitted bolts), I try to use a tool not a file. I'm not yet skilled enough to get really consistent results that way, and where there are multiple pieces close together, inconsistent features can look a bit naff.

Thanks Bill, yes that's why I put the "T" in brackets. Either way, there's nothing out there.

I do have the diamond shaped GT inserts, which I've put in my L/H, R/H and straight holders. They are my "go-to" tools for most materials these days. I just thought It would be nice to have a 45 degree chamfer tool in the same series though, since I already have the holder.

Yes, I can't find anything at all. It's a shame because it would be great for smaller workpieces.

I guess I could get the larger holder, but that kind of defeats the object.

All, a couple of years ago I was advised to try using ground GT inserts to get a decent finish on something or other (I think it was the stainless or silver steel valve rod on the Stuart 10V). Since then I've found that they give an excellent finish on most small components, in a range of materials from stainless steel to aluminium.

I have an ArcEuro square tool holder ( ARC SSDC-N 45° Turning Tool Holders - Arc Euro Trade , which I use for chamfering, but the standard insert (SCMT060204) seems a bit "blunt" for making very small cuts on small diameter work.

I'd like to use ground inserts in this tool, but Arc only seem to supply them in 9.525mm side lengths ( SCGT Square Uncoated Carbide Inserts - Arc Euro Trade , but I need 6.35mm length.

A Google search doesn't give any results for what I assume is the correct designation: SCGT 06(T)304.

Any ideas?

Thanks.

I got the bolts made today:

I used the end stop and gauges to get everything consistent:



Made a small fixture for getting the heads the same thickness, and the chamfers identical:



And a split fixture for the mill, to get the flat offsets identical:



All seemed to work OK:







After all that, they do assembly very snugly, so I don't thing soldering will be needed for the subsequent machining:



I might add some small 45 degree chamfers to the ends next to the bolts - I think they look a bit clunky as they are now. I was going to make them a semi-cylindrical radius, but the bolts aren't centred on the pads, so that might look a bit odd.

Unfortunately the I don't think there's enough room to make a flanged boss for the eccentric rod, so I'll stick with the rectangular ones as per the article.

Thanks Phil, yes the idea is to use the end mill again - I realise it's close to the edge, but at least the flaw tapers, so the very edge of it might get machined away anyway.

I'll see how it goes with the milling - I might just mill right through it it's possible. As you say whatever the inner end looks like, won't be visibe anyway.

Thanks Jason, I’m making some ‘fitted’ bolts at the moment, so depending on how they end up I might just bolt it.

I think the bearing pedestals are the same material as the straps, so I guess I could bore right through and plug to avoid any push-back, then machine?

Would it be possible to solder the plug in place rather than Loctite? I guess I’ll be soldering the joint faces anyway, so I could do the plug at the same time before final machining.

I don’t have any off-cuts, but I wonder if it’s the same material as the main bearing pedestals that I no longer need?

The other thing is I’m not that keen on the flat bar eccentric rods. I’ve seen some with parallel round bar screwed into a flat plate with a boss for the rod, the plate is in turn bolted to the eccentric. If I got some of the right diameter rod I might consider doing that, then I’d have the rectangular tail off-cuts spare.

I might see how much material I’d have for a pad on the eccentrics and take it from there.

Got the main flat surfaces completed on both straps, and machined the holes. Everything lines up fine, and all but one of the holes look to be good quality (at least when assembled using a twist drill as a spigot). The remaining hole has a slight bulge, but it’s cylindrical over about 270 degrees so it should be ok at least in function. I don’t think the holes are worth reaming after all:







I did notice a flaw in one of the halves, which I hadn’t picked up on before:



I don’t think it will machine out at the diameter specified. Is there any way of filling it before machining that wouldn’t be too obvious when finished (I won’t be painting the straps?

Anyway, next job is to make the four bolts from mild steel.

Thanks.

Hopper, yes the hole centres on the first strap are now OK, although one is slightly 'bulged'. It would be good to ream them as a pair (as Jason suggested initially), but obviously it's not great because they are now separate pieces. Since I already have a 1/8" reamer, I can't see a disadvantage?

I will bore the central hole once the fitted bolts are in place and tight.

I'm going to mill the holes in the second one later, because I can see no reason why drilling again would give better results this time. Unfortunately the mill isn't long enough to go through both at once, but the hard stop method worked fine.

Thanks Hopper. I think I'd like to try the fitted bolts - if nothing else it's another bit of machining to try.

I do already have a 1/8" reamer, so I wouldn't mind trying that. I've got a 3mm hole currently so it should be OK.

Is the best way of going about it to align the faces and one end face on a surface plate, temporarily bolt one side and then ream?

Thanks.

So I had a bit of time tonight, and tried the end mill and hard-stop method:



It seemed to work fine, with the holes moved in by 0.25mm. I'm thinking a 6BA thread and nuts might look better than 7BA - 6BA nuts fit pretty much perfectly on the footprint now:





I've been thinking again how I might have messed up the initial hole drillings, but I've concluded it must have been the drill wandering. With this in mind I think I might use this end-mill and hard stop method for the second one. Unfortunately the mill isn't long enough to go through both parts in one go, but it doesn't seem to matter. A 2.9 drill slies through ok, but a 3.01 drill won't. I wonder if a 3mm reamer would now align everything perfectly and make the fitted bolts easier to make?

The central hole is now pretty much spot-on in terms of circularity (or as good as it can be as a cast finish), so the 0.7 thick slitting saw seems to be the one to use.

OK. I might move the hole centres in by 0.25mm so if there’s a slight mis-match of the outer faces, I’ve got something to machine off if necessary.

I’ll just hope for the best with the main faces.

Thanks Jason.

That was my Option 1) above, but I assumed that the potential issue with re-boring the holes after splitting would be a mis-match of the faces and/or sides (since the point of a fitted bolt is to maintain precise alignment)? Obviously the centre hole isn't a problem because it will be bored.

I was going to make the bolts similar to what you 've shown, but with a square head which will be a good fit against the milled flat.

I do have a new 3mm end mill. Since it is short, I'd have to bore each hole in turn, from the mating face.

The only way I could do this accurately I think is by using an x-axis stop for the vice, where the parts are pushed against it, clamped, and the hole bored with everything locked apart from the z-axis. I'd have to turn the lower halves 180 degrees to make sure any side-to-side mis-match was compensated for (I think that would work) Obviously the supporting parallel would be removed just before the cutter broke through. Does that sound feasible?

Faces "A" & "B" below indicate the faces facing the camera, with the opposites facing the page, so when assembled "A"s and "B"s would go together.





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For the next one, I might try centering all four flats with the stub drill (as per previously), and drilling half way with a 2mm drill, then turn it over and centre the other end and drill.

Then drill with the 2.4mm drill all the way through. At least if the drill starts to wander, it might correct itself,,and the hole ends would be where they should be.

If it works I'd just buy another casting for the sake of £5. There wasn't much work in cleaning it up and facing it, so not much lost really.

These are the figures (blue is what they should be, Red what they are). The holes were actually measured from the non-joint line faces, so not as the sketch might imply:



They are for the hole centres and the abutments, measured from the centreline derived from each milled side.

It looks like the top is pretty much OK - very slight difference in abutment distance preventing the screw head from seating.

The right side hole goes through pretty much straight, and is OK.

However the left side seems to wander over towards the edge, and this is where my problem is, because the nut point overhangs.

The holes were drilled immediately after facing the sides, and in the same setup, facing the bolt head seatings on the spigot end, all in the same setup.

So I think the initial measurement was OK, and maybe the drill wandered - more on the left side?

By the way I think the offset error is about 0.007” - 0.010”.