GH Thomas Headstock Divider

[Allen Smithee]

So I have a 75% complete GH Thomas Headstock Divider for my Super7B, and I have the book and magazine articles which describe how to make and use it. I'm at the stage where I need to drill the two holes in the pulley/belt housing that mount it. GHT provides a template, some measurements and a couple of sentences on how to find the positions for these holes, but I guess I'm being thick because just can't grasp what he's on about. I can't see where/how the template is used, and what the datums are referenced to!

Can anyone who has built one of these give me any clues?

AS

[steamer]

I know there are a few here who have built one....Can you post a pic Allen?

Dave

[Allen Smithee]

Not from here - the data's at home.

I'm just trying to work out how the positions of these two holes are established - against what datums or reference points. The descriptiojs of the features in the book are vague and ambiguous to me (because I'm thick - I already know this!).

AS

[Don1966]

Hi Allen, I built the Dividing Head years back and it's here.http://www.modelenginemaker.com/index.php/topic,1460.165.html
If your talking about how to start the dividing plates You just start with one hole on a piece of metal and clamp to the blank dividing head and do the 60 hole plate first. After the 60 holes use the 60 hole plate with the micro attachment to complete the rest of the plate and the one you are using. You can start your holes at any point on the plate just scribe a line across and drill and start at this same point for the rest of the holes. The first set of holes which is the largest starts at the outer perimeter of the plate.  I have attached a calculation sheet for this head and the VDH. Good luck and I hope I answerd your question. the sheet calculates two ways one with the micro attachment and one with just the plate hole numbers.

Don

[Allen Smithee]

No, it's the more basic bit of how to find the position for the two holes in the Myford's pulley casing that take the pointed bolts which engage in the square bar that the whole thing is mounted on.

Looking at your thread you obviously felt this was a simple thing because you didn't mention anything about doing it (like I said - I'm thick!). But looking at your photos can you remember how you found the positions of the holes you drilled as in the attachment?

AS

[Don1966]

Allen I just used GHT'S dimensions and made a template to position the holes. I did miss drill one hole on the left back side and had to redo it. The front hole is quiet simple also just follow the directions. The back holes should position the attachment below the belt and you can get an idea by placing the attachment on the bull gear just to see how it fits, this will give you a in site of what you need to do. You pretty much have to play it.

Don

[Allen Smithee]

I guess what I just can't seem to grasp is what surfaces/edges the template goes against, and what the significance of the (1/16"?) cut out next to the 90 degree corner is? I'm sure when I funally get it I'll be slapping my head shouting "DOH!!" in embarrassment, but I'm not there yet...

 

AS

[tangler]

Hi AS,

It must be pushing 30years since I made my HDA.  I got the castings (3 lumps of CI) with the lathe but I'm pretty certain that the holes were already drilled in the countershaft casting.  I really can't see how the template helps. Here are some pics of mine.





My HDA  would appear to be mounted somewhat higher than Don's since my right hand hole is through the speed plate!

The only reference we have is the machined countershaft mount on the back of the headstock.  Everything else around there is a as-cast and somewhat variable.  The 1 1/2" dimension is horizontally rearward from this machined face on the back of the headstock (look at the side view on the GA drawing).  Height needs to be the same for both screws in relation to the line of the lathe spindle axis.  I'd be inclined to drill the left hand side so that the HDA cross bar avoids the belt and then mount the device on this end and with the worm engaged in the bull wheel, then let the spindle rotate until the HDA cross bar is horizontal - you can use a spirit level to get the bubble in the same position as it is when laid along the length of the lathe bed.  Then mark the position for the right hand screw. 

HTH,

Rod

[Don1966]

Allen the 1/16 notch you are referring to must be on the attachment it self. There is a notch you have to put on the main body of the attachment so the Micro Attachment can fit in snug to the gear. You will see this when you fit it.

Don

[Allen Smithee]

I think a penny might be teetering on the edge of the plummet...

I've beein assuming that the template is supposed to be used vertically in the outside face of the countershaft casting. Is it that I've completely misunderstood it, and the template should actually be laid flat on the top face of the flange of the countershaft casting with the long edge against the inside face of the countershaft casting?

AS

[Allen Smithee]

Allen the 1/16 notch you are referring to must be on the attachment it self. There is a notch you have to put on the main body of the attachment so the Micro Attachment can fit in snug to the gear. You will see this when you fit it.

Now that has really confused me!

From memory (because the book is at home and I'm not) - if you look at the drawing of the template it is essentially a right-angled triangle, but one side has a short rebate or "cut out bit" (techie term) next to the right-angled corner. I don't understand what this is for and feel that if I *did* understand it then the whole geometry would suddenly become obvious.

AS

[Don1966]

Allen I don't think the notch is relevant and if anything has to do with positioning into the corners of the lathe. Once you make it and place it into position you will see.

Don

[Allen Smithee]

Fair enough, but it exacerbates the problem - I can't see what position to place it in! 

I know I'm being really stupid, and when the penny finally drops I know I will be SO embarrased. But at the moment I think someone has put some loctite under the penny, because it's stuck firm!

AS

[Chipswitheverything]

Hi Guys, just to add to the general air of confusion here, here is a photo of my set up with the original Jack Radford design that was written up in one of the Model Engineer mags of the late 1960's.  I don't remember any information about templates in that write up -  as Don has suggested, it's more a matter of offering up and getting the LH end pinned down to a near as you can position with a screw though the casting, and working towards the positions of the other locators.  Haven't got GHT's write up to compare, but the Radford one was left initially so that the worm "main bar" was free to be shifted on the transverse bar at the back, so that the worm thread could be aligned with the lathe bull wheel - it was pinned and screwed later.  The latch at the front of the headstock is tackled last of the three location points, of course.   

Yours, Dave

[Don1966]

Allen if you have the book look on page 228 fig. 25.1 at the top is the triangle. The x on the triangle goes toward the back of the lathe itself vertically. The the 1/8 sets you height and 1/1/2 where the p is is your position to mark and drill your hole.

Don