• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Question: Best way to extract a broken screw from an RT-707 reel motor?

Ricktptman

Ricktptman

High Fidelity Enthusiast
Subscriber
I lucked across another 707 in otherwise near mint condition. (Locally, thank heavens.)

The only problem is the reel clamp screw is broken off. I've tried the smallest easy out I can find at the box store and I've broken TWO of the smallest bits I had (not super hard ones though and those screws are pretty high density) and still no luck. I don't want to (significantly) deform the end of the motor shaft. Has anybody had success attempting this?
 
Register to hide this ad
Some disassembly may be required.

Incidentally, density is relatively constant among steels. The factors affecting machining success are the alloy and hardness. I would guess that given the application, the screw is likely in the Rc 50-54 range. You will need a REAL drill, and not something from a chain store (Homo Depot or Harbor Frought). Get a source for Bendix or Hanson drills, and adjust the feed rate and cooling as necessary.
 
Post up a pic so we can see what you're working with.
A good machine shop can use an end mill to "drill" out the screw, leaving just bits of thread you can pick out with a dental pick. Last resort due to disassembly required and expense, but do-able. An end mill can drill into things that would cause a standard drill to skid off-center. Pick a job shop, or a gunsmith, where this skill set will be available. Not necessarily a CNC production shop.

It's likely not stuck due to corrosion if the rest of the deck is OK. More likely cross-threading, which will require some care to determine which part took the damage, the screw or receptacle. Wiggling back and forth (tightening first a bit, then loosening) will likely be of benefit.

If you go the left-hand drill direction, they are locally available in a small set at Harbor Freight, of all places. Many online options, of course.
 
I use left handed bits fairly often and have had a lot of luck with them. Nine times out of ten, when they break through, they back the screw out themselves.
 
Thanks for the suggestions. I meant to say "hardness" but I was in a bit of a hurry. Just FYI, the motor shaft "appeared" to me to deform more easily than the stump of the screw. It was SERIOUSLY stuck. Just to reiterate. I tried the reverse drill with bit approach before I posted this SOS. It came the closest to working, without actually doing so. The easy outs were a waste of time because they were all way too big. This one didn't go "my way". I did get the screw out in pieces, and the threads are pretty much destroyed. It was a low hours motor. I've never had an RTR motor go bad in a Pioneer machine. (Motor Caps, yes. Motors themselves, never.) I did the best I could with what I had at hand. Can't win 'em all, I guess. I have another motor. I just hate wasting a finite resource. The machine is pretty clean, with only moderate dust/schmutz inside along with a little bit of residue from (probably) Heating Oil. I cleaned the heads, circuit boards, and fascia/screws and they're drying now. The heads look nearly untouched. I cleaned the Pinch Roller and it looks brand new once I got the thin layer of Iron Oxide off it. Thanks again for the suggestions. Maybe I can use the motor to make a desk lamp or something... : - )
 
You can always drill and re-thread for the next size up. Jumping from metric to SAE may be a very small, easily managed change in diameter. Just be sure to label/color code things so you or the next guy gets the right screw on the right motor.
 
Thanks, Chip. That's a good idea. I might have to get a little help with that one. I wonder where one could find a match for an SAE screw with those parameters?
 
If it's M3 as Watthour surmises, you're going to be in SAE #4, 5, or 6 region, depending on how much you need to drill stuff out.
#4 and #6 are common hardware-store sizes, but #5 is less so. I recall they're used in gunsmithing on occasion.
Your process will be to jig it carefully and securely, re-drill to correct tap size for the closest of the above sizes that will fit (and that you can find the right machine screw type for -- flat head, fillister, round, whatever) and then carefully drill and tap. Have to be sure you don't run out of motor shaft diameter as you're upsizing, too. No offense, but based on your questions, it's probably not the right project to start this part of your education with... And there's no shame, just different skill sets and backgrounds. However, you can learn a lot by asking to watch and learn as it happens.

But before all this goes down, review how to keep the drilling chips out of the motor (which has magnets in it, I presume) and how to keep things squared up without damaging the shaft, etc.

Does this screw hold on the reel table? Or is it part of the reel keeper assembly? Or is it somewhere else, like a pulley or flywheel? (Haven't had the occasion to take my 707 apart, knock wood.)
 
91732a734p1-b01l.png


This may be among the better solutions, but it probably will require disassembling the motor, chucking the rotor/shaft in a lathe, and using a center drill to assure a straight finished thread.
 
You must log in or register to reply here.
Back
Top Bottom