Pinning topslide on ML7/Super 7

When I acquired my ML7 many years ago, the first thing I did was to convert it to the Super 7 type of topslide which allows a full 360 degree rotation. However I've noticed a problem. Under moderate loading there is a tendency for the slide base to rotate gradually. I could lean on the clamping screws but this seems an inelegant solution.

I was considering putting a pin, maybe a taper pin, through the topslide base into the cross slide. The idea being that you would accurately adjust the topslide to turn parallel and then pin it; so whenever you have the pin in place the slide will not rotate and will have been set to turn parallel. Of course you would have to remove it if you wanted a different angle, but most of the time the slide is used in the parallel position.

Has anybody tried this, or perhaps could point out a downside that I've not noticed?

Do you have the correct locking tapers in front of the screws?

I don't have any creep problems with my Super 7,

Regards,

Nick

They are left and right handed, I have no problems with rotational drift on my S7s

Actually I don't have locking tapers (I assume you are talking about plugs that head up the grubscrews) as this is a DIY conversion. I just have two 0BA grubscrews bearing on the mounting cone. Could be I need more beef in this area. Would still be interested in opinions on the pinning idea though -if only to get a repeatable parallel reset on the topslide.

Clive, taper pinning a swivelling head is common on industrial machines, so no reason why it would not work for you, I would suggest a taper pin with a male or female thread depending on diameter so you can extract it when required.

Chris Gunn

You mean one like this - has been on my 60 year old S7 for a long time. These days pliers are needed to remove it, hence gnarled appearance! The white bit is plastic channel to keep swarf out of the unused T-slot.

I would recommend you buy the proper tapered plugs to lock the topslide though.

Sorry, should have made the picture smaller.

Edited By Robbo on 04/09/2017 19:31:59

0BA grub screws pressing against the taper cone is a certain way to ruin it and chewing up the surface. You have little or no bearing surface you are pressing upon, hence movement. With the right use of the locking tapers in front of the screrw, you have considerably more area to press against.

Fortunately the cone shows little sign of damage. I wonder if the angular plugs are still available? I was thinking of exactly the setup in Robbos picture for the pin.

The plugs are available from Myford - **LINK** for the right hand one - don't forget they are handed left and right.

Probably just as effective would be a bit of brass round bar, say 3/4" long of 3/8", with the end cut off at a 60 degree angle. But is it worth the trouble at the price?

It certainly is...

O.K. ... I have to ask:

Is there really a difference between the Left and Right versions of this item

... or is it like having a left-handed teacup.

Myford lists two items, and uses pictures with different file-names

... but the two images are visually identical.

MichaelG.

[with an ML7R, so innocent in the ways of Super 7]

.

Edited By Michael Gilligan on 05/09/2017 08:17:18

That did occur to me.. The problem with the brass plugs is that, if you want to remove the topslide, they don't retract with the screws and the whole thing has to be wobbled and shaken until they decide to get out of the way.

Be wary of overtightening the standard Super 7 arrangement. The cross slide is weak at the point where the clamp holes intersect the top slide bore. On the 2 Super 7s I have had, both cross slides were bent at that point & required regrinding.

I only apply a slight nip to the clamp screws after regringing the cross slide to try & prevent a repeat & have not had an issue with the top slide moving under load.

It has been a while since I had mine apart, but I seem to recall that the ends of the clamp pads are cut differently - the use of one photo for two part listings is probably laziness, as the original Super 7 parts list has them as different part numbers and describes them as handed.

Nigel B

This is an interesting problem. My take on it would be that the original system of the screw clamps acting on bevel faced plugs draws the topslide down onto the surface of the cross slide an thus clamps it. With direct contact screws the action is more of 'nipping the' 45 deg taper of the topslide base especially after dimples have developed in it. Depends a little on the shape of the screw clamp ends. I would concur with some of the above suggestions that the way forwards is to complete the mod with the addition of the proper plugs. The other area for examination is the bearing surface on the underside of the topslide. In the course of things it will wear most towards the outside and eventualy end up round bottomed. This has the result of the clamping force being mainly in the centre where they have the least effect. Bluing the base will reveal this and a quick skim or even a spell with a scraper will rectify this.

regards Martin

"Is there really a difference between the Left and Right versions of this item"

Yes there is. Not visible in photographs, (and even difficult to see when you've got one in your hand) but there is a slight curve across the face of the plug, slightly diagonally, so that it seats on the topslide spigot properly. So the diagonal on the left hand is opposite to the one on the right hand. Because of the taper on spigot and plug the plug not only presses against the spigot but draws it down so the topslide is pressed against the crossslide.

What looks like a simple plug is quite cleverly thought out.

"Myford" descriptions are not the most accurate since they became a branch of RDG, so they may have used the same image.

Edited By Robbo on 05/09/2017 09:38:33

.

Thanks for that, Nigel [and Robbo]

... it says a lot.

MichaelG.

Edited By Michael Gilligan on 05/09/2017 09:39:06

Using an adaptor plate of the same dimensions as the taper cone of the topslide, the clamping force is strong enough to hold a swiveling vertical slide with dividing atachment in place. Usually the wheels I cut are small and this works better for me then clamping the vertical slide the normal way. Niko.

Edited By speelwerk on 05/09/2017 09:47:21

Here is my version of the taper pinned topslide:

I think I got the idea from Sparey's excellent book but couldn't find the reference just now. My small taper pin is rather fiddly and I have been meaning to install a larger one (the "meat" here is rather limited, however).

My machine is about the same age as Robbo's but is mutton dressed up as lamb; I went for Myford green when refinishing many years ago.

I, too, think that the thrust pads are handed and made the point about not inadvertently swapping them in a post in an earlier thread. The pads contact the male taper at a tangent, as it were.

Edited By ega on 05/09/2017 09:50:28

I couldn't initially see why the thrust pads should be handed, even if they were curved to match the cone of the topslide. Then it dawned on me that the clamping screws might not intersect the cone bore at 90 degrees. As I said, my setup is a DIY conversion from the old ML7, and I arranged the clamping screws to be at 90 degrees to the cone, so the plugs would be identical. I copied this arrangement from my Perris SL90. It does result in the RH screw being tricky to access and perhaps the setup on the S7 (which I haven't examined closely) is a bit different.

On my cheap Chineese lathe,I never have a problem with the top slide rotating .I just lock it in place and that,s it.

Maybe I,m just lucky ?

As an aside,I can cut a wide range of threads,both Whitworth and Metric,more than enough to meet my needs,together with a few UNF,from time to time. Lucky me.

Regarding Sparey, you wont go too far wrong with him ! his book is never too far away from my lathe. Might be an old book,but still delivers the goods and in simple terms.