Topics

Tek 485 volts / div knob

Steve Lindberg
 

I have a working 485 but one volts per division knob cracked and fell apart. Probably UV exposure.

Does anyone have one available?

Craig Cramb
 

Does anyone have one available?

Do you happen to know the part number?

Craig

Chuck Harris
 

If you happen to have the parts, they glue nicely using
a hobby shop solvent glue.

The reason they crack is the plastic shrinks, but the center
hub doesn't. That can be fixed easily. Put the knob pieces
back together around the hub, fitting them as best as you can.
Then take a small rubber band, and bind the pieces in tension
around the hub. Next, turn the knob up, and put your soldering
iron tip into the shaft hole and heat the insert. The instant
the pieces "fall into place", remove the heat and drop the knob
onto a shaft to help the insert cool quickly.

Now that the pieces are all fitting together without stress,
put a drop of solvent glue around the junction of the plastic and
the aluminum hub. This very thin solvent glue will wick into
the plastic cracks and weld them together.

Give it a few minutes to dry, and remove the rubber band, and
admire your handiwork.

-Chuck Harris

Steve Lindberg wrote:

I have a working 485 but one volts per division knob cracked and fell apart. Probably UV exposure.

Does anyone have one available?



n4buq
 

Same kind of problem is prevalent in the (Delrin?) gears inside older HP equipment - particularly the 8640B. I've resorted to removing the hub, boring the hole a tiny bit larger, and then gluing (epoxying) it all back together. Hadn't thought of melting the plastic with the heat of the hub. Nice idea.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Chuck Harris" <cfharris@...>
To: TekScopes@groups.io
Sent: Friday, July 19, 2019 7:33:57 AM
Subject: Re: [TekScopes] Tek 485 volts / div knob

If you happen to have the parts, they glue nicely using
a hobby shop solvent glue.

The reason they crack is the plastic shrinks, but the center
hub doesn't. That can be fixed easily. Put the knob pieces
back together around the hub, fitting them as best as you can.
Then take a small rubber band, and bind the pieces in tension
around the hub. Next, turn the knob up, and put your soldering
iron tip into the shaft hole and heat the insert. The instant
the pieces "fall into place", remove the heat and drop the knob
onto a shaft to help the insert cool quickly.

Now that the pieces are all fitting together without stress,
put a drop of solvent glue around the junction of the plastic and
the aluminum hub. This very thin solvent glue will wick into
the plastic cracks and weld them together.

Give it a few minutes to dry, and remove the rubber band, and
admire your handiwork.

-Chuck Harris

Steve Lindberg wrote:
I have a working 485 but one volts per division knob cracked and fell
apart. Probably UV exposure.

Does anyone have one available?





 

On Fri, Jul 19, 2019 at 02:33 PM, Chuck Harris wrote:


put your soldering iron tip into the shaft hole and heat the insert
Neat!

Raymond

Chuck Harris
 

With delrin gears, I use the same heat trick, but I also
play dentist with the gear to strengthen it a bit. If the
gear is big enough, I drill tiny holes on either side of the
crack in the flat part of the gear, and suture them together
using thin steel wire. Once the gear is stabilized, and presents
good fitting teeth around the crack, I use a dremel tool and a
small carbide burr, and cut a channel in the hub near where the
flat part of the gear joins. I suture that channel with thin
steel wire wraps. As the final step, I put JBWeld epoxy over
the sutures to stabilize them, and strengthen them.

If the gear is too small for the suture holes, I cut the groove
around the hub, and wrap it, and then apply the JBWeld epoxy.

I have even gone so far as to fashion a replacement tooth, and
dovetail it into the gear, and fine tune it with a file... but
that was a very desperate time...

I have never had a second failure.

-Chuck Harris

n4buq wrote:

Same kind of problem is prevalent in the (Delrin?) gears inside older HP equipment - particularly the 8640B. I've resorted to removing the hub, boring the hole a tiny bit larger, and then gluing (epoxying) it all back together. Hadn't thought of melting the plastic with the heat of the hub. Nice idea.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Chuck Harris" <cfharris@...>
To: TekScopes@groups.io
Sent: Friday, July 19, 2019 7:33:57 AM
Subject: Re: [TekScopes] Tek 485 volts / div knob

If you happen to have the parts, they glue nicely using
a hobby shop solvent glue.

The reason they crack is the plastic shrinks, but the center
hub doesn't. That can be fixed easily. Put the knob pieces
back together around the hub, fitting them as best as you can.
Then take a small rubber band, and bind the pieces in tension
around the hub. Next, turn the knob up, and put your soldering
iron tip into the shaft hole and heat the insert. The instant
the pieces "fall into place", remove the heat and drop the knob
onto a shaft to help the insert cool quickly.

Now that the pieces are all fitting together without stress,
put a drop of solvent glue around the junction of the plastic and
the aluminum hub. This very thin solvent glue will wick into
the plastic cracks and weld them together.

Give it a few minutes to dry, and remove the rubber band, and
admire your handiwork.

-Chuck Harris