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Colchester capstan tooling queries

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Ian Parkin21/04/2015 09:31:52
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dsc00332 (medium).jpgdsc00329 (medium).jpgI have just aquired a capstan attachment for my lathe

I wanted it to use with a coventry die holder and for drilling jobs

how do I mount tooling?

theres 4 3/4" holes and 1 1" hole

I have made some 3/4" spindles to hold tools but what does the cam lock bolt look like....they were all missing

I made those slugs with a length of 31/64ths silver steel and machined away a 3/4" diameter bit to lock the holder in...just need tapping on top so a nut can pull it up.

Is this how it works?

But how to do the 1" hole as theres hardly any material left when i've cut a 1" scallop out

does anyone have one to show me what it should look like

Ian

dsc00328 (medium).jpg

Andrew Johnston21/04/2015 09:56:53
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Posted by Ian Parkin on 21/04/2015 09:31:52:

Is this how it works?

But how to do the 1" hole as theres hardly any material left when i've cut a 1" scallop out

In a word, yes. That's how my various capstan units work. However, my capstan units have uniform hole sizes. I wonder if a previous owner has bored out a couple of holes to fit existing tooling? Give it a go, at least the clamping bolt is fully supported so it won't bend.

Andrew

JasonB21/04/2015 10:04:20
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Do you actually have a need to mount 1" tooling? If not you could make a 1" to 3/4" sleeve and notch out the side so the same size camlocks can be used that bear on the 3/4" shank of the tool.

Ian P21/04/2015 10:13:20
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Regarding the clamp for the oversize hole. If the body material is not hard (presumably not if its already been bored out) then you could enlarge the existing clamp hole but offsetting it to a new position. You might need to be creative to mount the body at the correct angle but could use an end mill to bore the new hole or it could even be done on the lathe with a single point boring tool.

In reality the bore diameter and the precise angle and position are not very critical as you will be making the clamp to fit.

One possible quicker/simpler method might be to drill and tap two new holes either side of the existing clamp bore and have a bridge plate press 'down' on the clamp rather than having to rely on pulling up on something that almost necked through.

Ian P

Capstan Speaking21/04/2015 11:16:25
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You need to split the pinch cam with a big gap. They then have a shallower cut-out and a tapped hole in the bottom part for a screw. They actually "float" in the hole and pull together.

The parallel holes are for a parallel o/d morse socket. These are widely available.

Saxalby21/04/2015 11:36:22
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Ian,

You asked what the locking bolts / cams looked like. Here is a picture of the tooling lock bolts on my Boxford capstan unit.

capstan unit.jpg

Ian Parkin21/04/2015 12:16:20
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Capstan speaking...That idea is used on startrite and fobco drilling machines for the tables and head but without a cut out in my tooling for the bolt it wont work on here...or does the tooling have a space cut out for the bolt to pass through?

Saxalby ...that looks just what i'm doing thanks for the picture is your tooling a parellel shank?

Jason...my coventry head has a 1" shank

Many thanks for the other answers

Ian

Saxalby21/04/2015 12:40:48
174 forum posts
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Ian,

Yes the tooling shanks are 3/4" parallel.

Never had problem finding tooling at boot sales etc.

Barry

Capstan Speaking21/04/2015 12:50:29
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On a real capstan the clamp hole is offset enough for a pinch screw to pass by. This is done in a cast adaptor bolted to the capstan.

lotimage_26259.jpg

If the clamp cam were one piece it may as well be what we British call a cotter pin or taper pin. The cut-out would be pointless except at the bottom. The morse socket is not adapted and would be seriously hard anyway.

Such a one-piece arrangement would put enormous load on the thinned section which may explain why the are so few pins remaining.

Most load is inward anyway so perhaps it could work. You need enough grip to pull a swarfed up drill out or to trip a die head.

Case hardening is the way to go or it will only be a matter of time before it snaps.

duncan webster21/04/2015 22:01:59
3710 forum posts
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Just an idea, which might not work. Make your cotter with it's scollop, but instead of a turned down bit at the top, drill it right through on the axis, tap the bottom end and drill the top end clearance. Then cut it in half so you have 2 bits with 1/4 circles cut out. Then on your 1" shank cut out a half moon to clear the bolt which you are going to pass through the top bit into the bottom bit. It means you have to fully remove the bolt to change tools.

Otherwise, can you make up a bush and loctite it in to restore the 3/4" dimension

ronan walsh21/04/2015 22:32:14
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Is that a neracar in your avatar Ian ?

Bazyle22/04/2015 00:16:14
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I have a tool with a variation of the two part cotter because the screw would be too small or would have a chunk cut out of it preventing rotation. The bottom section is integral with the shaft which is screwed at the top. The second half is a thick tube over the shaft and clemped with a nut. The assembly is then cut to take out the scallop which cuts into the shaft aswell. This enables the shaft part to be thicker than if made as a screwed rod as described by Duncan.

Ian Parkin22/04/2015 12:22:16
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995 forum posts
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Ronan

Yes its a model c ner a car

the capstan head with the 1" hole has been bored wrong

the seller insists that it came factory bored 1 1" and 4 3/4"

it certainly looks well done but all the 3/4 holes line up on centre but the 1" is down on centre height

so I may need to plug and rebore

theres not enough space below the diameter of the 1" hole to do as duncan or bazyle suggests without drilling deeper

its a shame because I wanted a 1" size for my die head

Ian Parkin22/04/2015 13:28:41
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Job sorted

the seller came round with an attachment head that bolts on to the top of my capstan and has 5 1" holes in it with all cam locks present

looks in fine condition so I'm well pleased now

Ian

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