Paul

Dimensions vary according to motor power and year the head was made. I made a new set to replace the turquoise bushes in my mid 1970's head with 1.5 HP motor. If yours is same power and has same colour bushes I can send you a PDF of the drawings. Note that the turquoise bushes appear to have been moulded in place then bored as there is a retention ridge halfway along fitting into a mating recess in the pulley which makes life complicated when going for an exact fit. Mine fit and work fine using loctite to retain them but I suspect the ridge is a little undersize in its groove. Some guessing involved in reverse engineering as mine came out is several parts and I never did find them all.

Later ones than mine have simple plain bushes which are easily reverse engineered. These are the ones the US kits are for. Sorry I don't know what year the change occurred, i think it likely that you have plain bushes.

Clive

Depends whether it was a Monday morning machine or a Friday afternoon machine

Seriously though it does depend a lot on models, horsepower, where made i.e. the licensed models etc.

Some are on 24mm motor shaft size, some on 28mm shaft size but of those 28mm ones some are on 7mm wide keys and some on 8mm wide keys and to muddy the waters still further some have different sized tail bearings.

When they wear bad they wreck the motor shaft. Typical varispeed motor rotor.

Top diameter of 29mm is OK as this is the fixed sheave but the 28mm diameter bit where the sliding sheave runs is toast and a new rotor is about £400.

Soooooooooooo.

Gobo some weld on it, don't talk to me about distorsion, and wait for the weld to dry.

[Note to self : Self, – remember to pick up by the other end ]

Once the weld has dried this is lurking under all the slag and crap.

Two hours, start to finish and another bridgeport lives to bend another day.

John S. [ who much preferes step speed models with a VFD. ]

[ EDIT ] BTW I this is not uncommon, I probably do between 15 and 20 per year.

Edited By John Stevenson on 27/09/2012 17:31:30

I sure hope there's no carbon migration at the weld zone inside those shafts. Any preheat used before welding? Are you using a high purity rod?

JD

Paul

No problem to send the PDF drawing. Where do I send it?

Do remember to check it against your machine before following as its amended but untested. I corrected the errors in the original reverse engineered drawing to match what actually fitted but I haven't made another set to check. Making is a horrible job due to the thin wall and uncertainty as to how much the delrin will spring when you make them. Can't make turquoise style ones thick and bore out after fitting because they need to be very flexi to get in.

Pictures of the making process too if you want. Was going to write it up for MEW but first draft was so bad …..

Dunno what grade of loctite I used to stick them in with.  Probably one of the high strength ones (green?).

Clive

Edited By Clive Foster on 27/09/2012 22:00:59

Jeff,

It's only when you get on to quite large or special motors that they use anything other than basic mild steel.

A lot of the smaller motors even use leaded steel.

The licorice reference was made that although Bridgeports have a large following they are a lot like Myford in that the machines is not as robust as the name. There are a lot better out there and usually for less money.

James

General recommendation is a high strength cyanoacrylate with a suitable primer to modify the Delrin surface and promote adhesion. For example :- **LINK** .

I've done well enough using ordinary cyanoacrylates and high strength loctite to retain simple bushes after lightly abrading the Delrin surface first. My shop made Delrin replacements for the turquoise "moulded in place" Varidisk bushings appear to be holding in there just fine. 6 years and counting! I doubt that it would be strong enough to hold a stressed joint though.

Maybe this stuff **LINK**. is the real deal. Says its for Delrin on the blurb. But being an epoxy I wonder if the joint line may be too thick for Varidisk bush retention.

Clive.

Edited By Clive Foster on 27/03/2018 09:28:39

The key to bonding CA adhesives to "shiny" plastics is the polyolefin primer (aka "adhesion promoter" ). That Bondloc stuff (KWIL) and the "POP" product mentioned in the Permabond site appear to use such a primer. Note that the page for the POP product on the crap Permabond site is broken….

Google "polyolefin primer" and you get loads of hits, including the Loctite 770, Permabond POP and others. It's useful stuff to have handy, as it allows your existing selection of CA adhesives to be used on shiny plastics in applications such as this.

Murray

Edited By Muzzer on 27/03/2018 13:23:59

It's nice to see John Stevenson still giving advice.