HH. Grinding rest

[John Rudd]

Gents,

I started building Harold Hall's grinding rest........


I've hit upon a problem...
Having cut the dovetails for the lower slide block and the two 16mm thick slide swivel pieces, I find that when I offer up the lower slide to either of the swivel blocks, there is little support on one side of the dovetail.... The side where the gib strip goes..

I'll try a picture later to hopefully explain better


Anyone I any idea what's gone wrong? What have I missed ?

[vtsteam]

Looks like there should be about 5mm of metal there. Is that what you have?

(nope, that's wrong..........hang on, checking....)

I make it out to 5.38 mm.  If your piece width is under 50mm it will reduce that.

Do you have 10 mm at the top of the dovetail?

[John Rudd]

ok,

Here's a crap-o-cad sketch of how it's fitting together.....and how it doesnt work out....
Basically if I offer up the lower slide and insert it into the swivel block, the side where the gib strip goes has virtually no landing area supporting the lower slide

[DavidA]

John,

What is the MEW issue number for this item (or are use building it from another source) ?

Dave.

[John Rudd]

Its from HH's book ...'Milling a complete cock upcourse'

[vtsteam]

John, I have the book, too. Can you check these dimensions on your part?

[ziggar]

if you've made it to plan as the book shows, and all your sizes are correct, then it should all be just dandy once you make the gib strip and put that in the assembly as required

i made one and it all works and fits as it should do

[John Rudd]

John, I have the book, too. Can you check these dimensions on your part?

Vt, thanks for sense checking.....I away for the weekend atm but will check when I get home
Ziggar

Thanks for the confidence boost....again, I'll see once it's all finished


Onwards and upwards.....

[vtsteam]

Also, John,

The lower slide dovetail appears to be 8.5 mm deep. (it would be easy to misread the tiny dwg and make them 6mm deep)

The slide swivel pieces appear to be 8mm deep.

I'm having a hard time visualizing the finished assembly, even with the assembly drawing, but it seems like the dovetails would therefore ride on the bottom rather than the shoulders.

[John Rudd]

When I return home I'll take photo which should make things clearer

[Chuck in E. TN]

I have one 90% completed. Working out how to attach the table. I had issues with the dovetail parts but have them all working now. I can take pics if needed. I strayed from the plans as my materials were imperial, but I worked to the drawings, converting dimentions from the metric to imperial.
Chuck

[John Rudd]

Right, here's a few shots of what I'm trying to do.......

Chuck some of your fotos would be good for comparison please......

As can be seen from the second foto, not much support on the right where the gib goes.....

[vtsteam]

John, as I said before, shouldn't it be that the dovetail (male part) should be riding on the bottom, not the shoulder? Therefore zero support there -- instead there should be vertical clearance, and the shoulder width is irrelevant.

According to the drawing, the male part is 8.5 mm  deep, while the female part is 8 mm deep. Or have I got that wrong?

[ziggar]

when people stray from the sequence in the book is when they start having trouble. such as parts not fitting, parts not lining up, and other seemingly insurmountable problems. Ive seen other 'experts' on other forums complaining that handles dont fit and this that and the other doesnt fit or work, but they have ALL been trying to do it they're way.

when i made mine i absolutely knew nothing [pretty much the same now if im honest] so i followed the book word for word.  It is after all aimed at the beginners to the hobby. I didnt stray one syllable from the text or the drawings, and everything worked exactly as Harold said it would. Everything lined up spot on. Everything worked as expected. And absolutely NO problems at all assembling all the parts. I made it using a Sieg C1 lathe and a Sieg SX1 mill.

You have to trust the text and believe that it will all work out the way its supposed to. It will, if you follow the route as printed and dont try to jump ahead and do things out of sequence.

and if i remember rightly [cos i cant be arsed to look at the book right now] the 8mm and 8.5mm measurements are correct.

[John Rudd]

John, as I said before, shouldn't it be that the dovetail (male part) should be riding on the bottom, not the shoulder? Therefore zero support there -- instead there should be vertical clearance, and the shoulder width is irrelevant.

According to the drawing, the male part is 8.5 mm  deep, while the female part is 8 mm deep. Or have I got that wrong?

vt,

You could be right and I'm looking to resolve a problem that doesnt exist.......

Maybe I ought to drop HH an email ask him directly.....   ?   

[vtsteam]

Could be a mistake on the drawing, or could be intentional.

It's possible that on a small dovetail like this the intent was to ride on the bottom since it was likely it would be clamped a lot, ant that would give better clamping area - resistance.

[DavidA]

I don't want to look too silly here,  but it appears to me to be upside down.  Surely the contact should be on the slope. And the gib stip should make this happen.

Unfortunately all my MEW issues are packed away somewhere so I can't check it.

Dave

[ziggar]

it IS upside down
the larger squarer piece should be the uppermost part

if you look at the photo of the completed article here http://homews.co.uk/page145.html you can plainly see how it relates to the whole.

[RussellT]

I think it's OK John.

The picture here

http://homews.co.uk/LrgGrindRest01.jpg

clearly shows exactly the same issue you have noticed.

Russell

[vtsteam]

Here are the relevant dwg details, so people can stop guessing. And in the photo above it looks as if, yes the dovetail is not intended to ride on the shoulder, but on the bottom (or top, depending on which slide you are referring to -- there are 2, and in opposite orientations).

John, it looks like you may have reversed the 8 and 8.5mm depths, since yours doesn't seat on the bottom.

[vtsteam]

I don't want to look too silly here,  but it appears to me to be upside down.  Surely the contact should be on the slope. And the gib stip should make this happen.
Dave

it IS upside down
the larger squarer piece should be the uppermost part

It doesn't make any difference whether he sets it upside up or upside down on a workbench for the purpose of a photograph. We're talking about a fit of two parts.

Yes a gib ALWAYS forces a dovetail to contact the opposite slope, AND either the shoulders OR the bottom of the slot, depending on the intent of the designer. In this case, according to the drawings, it's the bottom. In the case of most dovetail slides on the lathes I have seen, it's on the shoulder.

For most dovetails, using the shoulders as bearing surfaces reduces friction when sliding. Using the bottom (or base) of the dovetail increases friction, but that may be an advantage where you intend to lock a short part into its ways.

[flutedchamber]

Could someone please tell me where I can find the original Harold Hall post about the grinding rest?  I can't find it using the search feature.

Thank you.

[flutedchamber]

Found it...

[John Rudd]

Had another think about this.....
The 8.5mm depth on the lower slide is fixed by the angle and across top dimension of 32mm....
So having cut the swivel plate angles too, with the 10mm width on one side again, there is correlation between the angle and depth...

So I think I'm looking for a problem when there isn't one, plus I've looked at the book again and have a warm feeling abou it all ...

But I'll wait from the Maestro Himself

I'll post his response once I have it......This should resolve all..

[Metalman]

I have over the years had a number of questions regarding the grinding rest that result from the very small scale of the assembly drawing in the book. Because of this, I added to my website some time back an enlarged assembly drawing of the top half of the rest. This can be found at http://www.homews.co.uk/page145.html. The link being in the bottom line of the text.

If there is any one reading this thread that are unaware of my website the home page is at http://www.homews.co.uk/index.html but the best place to start for the metalworking content (now around 500 pages)  is at the book style index at http://www.homews.co.uk/page463.html

Also, I have started to add galleries showing a number of setups for a given situation, typically, Using the faceplate. The index for these is at http://www.homews.co.uk/page542.html there are though a lot more to come.

I would add that I have already mailed John directly with some help and telling him about the larger drawing which should answer his questions.

Harold Hall

[mattinker]

Harold,

thanks for the links to your site, I've got a lot of reading to do now!

Regards, Matthew

[John Rudd]

Well, received an email from Harold, What a star! 

He pointed out that the contact points are the two flat surfaces....So no issue. I can plough on with the rest of it...