GHThomas Versatile Dividing Head

[derek hall 1Participant @derekhall1]

Hi everyone,

Just got to the stage of finishing the casting body, and now about to m/c the main sleeve. Now GHT says that this sleeve has a bore of 3/4 inch and this is then reduced down to smaller bores by making additional split sleeves, the whole lot clamped together by 3 small grub screws bearing on copper pads.

Now this seems an awful lot of extra machining and swarf generation so make these additional split sleeves, so I was wondering if I should modify the main sleeve to take a ER style collet chuck and invest in some suitable ER collets or something similar?

I have no collets of any type at all in my workshop, most of what I do is making tools, stationery engines and clock making and repairs.

So if anyone as any advice as to what I should do, eg stick with the original 30 year design or if anyone has modified their VDH to suit then I will be interested to know!

By the way if I go down the ER collet route what size should I consider?

Best wishes

Del

[derek hall 1Participant @derekhall1]

[Roderick JenkinsParticipant @roderickjenkins93242]

Del,

My dividing head is a Timmins, rather than the VDH, and has a 2Mt and the Myford nose to suit my lathe chucks. I have made the HDA though and used the plates and fingers on my Timmins head. Mostly I use the Myford patent collets which have a range from 1/16" to 1/2" in my dividing head. If I were making a VDH I would certainly go for ER collets. GHT mentions collets in the write up but dismisses them as being too expensive – ER collets weren't readily available from the far east then. You could either make a spindle with an ER nose or you might like to consider one of the ER chucks which are available with a parallel shank. My workshop tasks are similar to yours and ER 25 suits me with a range of 1-16mm. ER 32 goes from 2-20mm. I would consider what size I would use in my other machines though, ER collets are very versatile.

HTH

Rod

Edited By Roderick Jenkins on 13/08/2015 13:43:46

[Thor 🇳🇴Participant @thor]

Hi Derek,

I haven't made a VDH, but I have used a ER-32 chuck with a plain 25mm dia. shank as the mandrel in a grinding jig I am working on. IIRC the VDH bore is over 1 in. so you may need to make a sleeve to use such a chuck. Another option is to make your own mandrel that fit the VDH and with a taper that accepts the ER collet size you want.

I use ER-16 and ER-32 collets in my workshop.

Thor

Edited By Thor on 13/08/2015 17:16:42

[AjohnwParticipant @ajohnw51620]

The reason he uses a long plain hole is down to precision and the ease of making adapters.

Collets sound great but SHOULD be specified for run out 50mm from the opening. The advantage of the long hole is that it's all set by the length of the part in it and the clearance. The clearance can be very small. It's pretty astute of him actually and aimed at model engineers working at home and making most things themselves rather than buying and not just using it for gears. If I remember correctly he mentions considering it.

Personally I would add a spindle nose to it. Mine has a Myford nose and I use a boxford so I have a 3 morse to myford adapter and a draw bar for it. It also has a 2 morse socket which basically means I would have to make taper adapter or buy and hope they are decent quality.

As Rod mentions you could buy a straight shank er25 collet holder. They are available with a 3/4" shank also 25mm or 1" but they always seem to be undersized. Or even put an ER on the end but I would still retain an accurate hole behind it.

John

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[derek hall 1Participant @derekhall1]

Thanks so much for your replies and advice…what a great forum this is!

Del

[Michael BelferParticipant @michaelbelfer47979]

I have a set of Hemingway castings, gears, worms, and div plate blanks for sale. In Australia, these have been ageing for so long I cant see myself making the GHT head so they are for sale at 2/3 of current sale price plus shipping to wherever

Michael dow nunda

[Author]

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