Brass Gears for the HP 8640B Signal Generator

Description

Update 3rd April 2021. A fresh batch is in.
On offer are custom-fabricated brass gears for the HP/Agilent 8640B signal generator. A well known weak point of this generator is the gear
train connected to the frequency range switch. The
gears are made of Delrin with a brass insert. Over the years they have tended to shrink and
split. You probably already know that if you have one of these beautiful generators!
I had the original delrin gear from my ~1983 instrument 3D-scanned and reproduced in a machine shop using a semi-automatic process with custom jigs and fixtures. These are practically exact replicas of the
original 1983 gears
, and will work just as well with no more splitting or cracking!  I have sold several of these sets on eBay earlier and have now got a new lot fabricated. Check my feedback and bid with confidence!
A full set of 3 gears (2xCombo + 1xSpur) will replace all the 3 gears that suffer from this problem – for just $55 plus S&H worldwide!
I
am listing these in quantities of 5 each, so I can give myself time to
handle the orders. If you need to buy a complete set and the quantity
shows zero, there is no need to buy the gears separately – I do have
several sets in stock and usually update the quantities once every few days.
As some of the machining process is manual, please be aware that there are very small cosmetic blemishes on the gears which are in fact barely visible and do not affect their functioning (see close-up photo).
The set screws required are #4-40 (the same size as the original). I usually include 4 of them if you order a set; they are 1/4″ in length (a bit longer than the original) –
however as of Sep 18 2020 these are temporarily unavailable and I will not be including set screws
.
A video of these gears in action is available on YouTube at https://www.youtube.com/watch?v=q1H-ieO9uYw.
Any questions, please ask, especially if you need multiple of just one type such as Combos, or some other bespoke combination. For example I can offer a set of 3 combos for $60 + S&H.
Important notes
:
1. If
you find the movement seems a tad stiff or squeaky with these gears, do
NOT immediately try to enlarge the hole or reshape any teeth! Some stiffness is
natural when metal meets metal – use a drop of machine oil on the shaft
and/or teeth – this usually works wonders. Also make sure you read the
“A9 Reassembly” section in the 8640B manual which has advice on what to
do if the gear shafts bind causing movement to become stiff. Be prepared
for 30+ minutes’ worth of fine-tuning of the gear assembly before
things hit the sweet spot.
2. On occasion some gears may not slide easily onto the shaft at first shot. This is because of manufacturing tolerances and/or small burrs in the gear hole. If this happens, here is what works: just take some coarse sandpaper (#60-80), make a roll and run it inside the shaft for about a minute or two. Blow away the dust from the shaft and screwholes, swish it in some alcohol if you like, and it will fit perfectly.
Ships from Bangalore India using eBay India’s global shipping program. S&H shown is for one set of 3 – just $15 to anywhere in the world, and just $5 for each additional set in the same order. If ordering a bespoke combination of gears please purchase
but DO NOT PAY – ask for an invoice so I can combine shipping suitably
. Duties and taxes are the buyer’s responsibility. Note: Standard shipping from India normally takes 12-15 biz days, but I have listed it as Economy shipping from India to make some allowance for the delays that are currently being experienced with a small proportion of packages. Please be patient!
Thanks and good luck with your 8640B restoration!