Jump to content


Photo

Boring a counterweight?

  • Please log in to reply
21 replies to this topic

#1 bykhed

bykhed

    Viking 1

  • *****
  • Posts: 792
  • Joined: 22 Oct 2007
  • Loc: Westminster, CO

Posted 26 March 2013 - 09:51 AM

Quick question: I have a cast iron counterweight with a bore diameter that is a bit too small for my use. Would it be possible to bore the counterweight with a standard drill press and bit? Thanks!

-Matt

#2 Mike I. Jones

Mike I. Jones

    Gemini

  • *****
  • Posts: 3214
  • Joined: 02 Jul 2006
  • Loc: Fort Worth TX

Posted 26 March 2013 - 09:57 AM

To what inside diameter? Boring will always give a smoother finish if the boring bar cutter is ground properly, the cutter angle is right for the metal, and the feed rate and depth is not too ferocious.

Drilling an ID much larger than 1/2" on a drill press is not advisable. I routinely drill to 1" ID for bore bar clearance, but in my lathe, not on a drill press.
Mike

#3 JWW

JWW

    Apollo

  • *****
  • Posts: 1392
  • Joined: 12 Dec 2005
  • Loc: Arizona or Mexico hard to tell

Posted 26 March 2013 - 11:01 AM

My 2 cents, assuming no challenges like chill spots that will wreck any cutting operation, cast iron is very easy to machine and tap. However I don't have a drill press but a Bridgeport and lathe instead. I would "think" that if you are only increasing the size a touch that a drill press would work fine as long as you have the counterweight held down securely/safely, use the proper speed/feed and a super sharp drill. If you end up loosing a finger or something, don't blame me for YOU not being safe.

-JWW:

#4 oldtimer

oldtimer

    Apollo

  • *****
  • Posts: 1331
  • Joined: 13 Nov 2008
  • Loc: Lake County Illinois

Posted 26 March 2013 - 11:33 AM

I have bored many cast iron counter weights by simply locking them in a vice and using a standard hand drill. As long as there is an orginal pilot hole oversize drilling has never been a problem.

#5 bremms

bremms

    Mercury-Atlas

  • *****
  • Posts: 2588
  • Joined: 31 Aug 2012
  • Loc: SC

Posted 26 March 2013 - 11:36 AM

Yes it can be done, I have done such things. But , if you don't have a lot of experience doing this kind of thing by hand you could get hurt. I would put the counterweight in a strong vise use a hand drill with a large handle. If you don't have a strong milling vise doing this on a drill press is not a good idea.
Use good judgement and please don't injure yourself.

#6 kfrederick

kfrederick

    Gemini

  • *****
  • Posts: 3006
  • Joined: 01 Feb 2008

Posted 26 March 2013 - 12:04 PM

If only a small amount needs removed a half round file and some elbow grease might work.

#7 Fuzzystar

Fuzzystar

    Lift Off

  • *****
  • Posts: 4
  • Joined: 15 Sep 2009
  • Loc: Palatine, Illinois

Posted 26 March 2013 - 12:22 PM

I encountered the same issue.
I don't own or know how to use a metal cutting lathe. I envy those that do have one and know how to use it.
I have a GM8. The counterweight shaft is 1.25" diameter.
I had a iron weight from a barbell set that was ~2 - 2.5 lbs. (I don't remember). I'm at work during my lunch.

I used a drum sander (I think it was ~ 1 inch) that you attatch sandpaper to. This was attached to my table top drill press. I initially used 100grit.
After some initial ID sanding,
I 'tested to see how close I was to the 1.25" by seeing if it would slip over the counterweight shaft. Initially of course it didn't. I took an old 35mm film canister, slobbered black marker all over it and rubbed it inside the hole of the weight to mark the high spots. I repeated the process until the weight slipped over the counterweight shaft.
I mounted the counterweight to the counterweight shaft using PVC 1.25 compression fittings on either side.

#8 Ajohn

Ajohn

    Mariner 2

  • *****
  • Posts: 283
  • Joined: 03 Dec 2007

Posted 26 March 2013 - 02:26 PM

A lot depends on the material the weight is made of. Cast iron can be so hard that an hss drill won't touch it. You could probably tell if that is likely to be a problem if you use a small file on the corner of the bore. If it files fairly easily an hss drill should be ok with a slow feed and not too high a speed.

Anything else is hard to say really without some info on the bench drill and size of the hole. Say it was a small chinese one with no morse taper holding the chuck or 2 morse and a rather large chuck for that size mainly intended for wood work it might struggle enlarging a 3/4 hole slightly.

One thing for sure you will need to hold it firmly with the vice clamped to the table of the machine or at least in a way it can't rotate. A decent industrial drill vice should be ok providing you make a flat on one side to ensure the work doesn't rotate.

John
-

#9 Norm Meyer

Norm Meyer

    Mariner 2

  • *****
  • Posts: 252
  • Joined: 08 Feb 2009
  • Loc: Warren, ME 04864

Posted 26 March 2013 - 02:53 PM

bykhed,
What kind of CI counter weight is it? Is it like an edmund
or losmandy or is it just a barbell weight? How heavy is it?
If it is just a barbell weight I have some here already and
I'll bore one to size for you just pay the shipping and it's yours. If it is a fancier one you could ship it to me and I'll bore it to size. But you'd have to pay shipping both ways, I won't charge for the boring.

Norm

#10 John Carruthers

John Carruthers

    Skiprat

  • *****
  • Posts: 3545
  • Joined: 02 Feb 2007
  • Loc: Kent, UK

Posted 27 March 2013 - 03:40 AM

I made up a small fly cutter that I use in a drill press or on the lathe, if you take light cuts you may be ok.
fly cutter drawing

Attached Files



#11 GlennLeDrew  Happy Birthday!

GlennLeDrew

    Voyager 1

  • *****
  • Posts: 10643
  • Joined: 17 Jun 2008
  • Loc: Ottawa, Ontario, Canada

Posted 27 March 2013 - 05:33 AM

I bore my counterweights by nattering on about cosmology and quantum mechanics. :grin:

#12 Geo.

Geo.

    Mercury-Atlas

  • *****
  • Posts: 2840
  • Joined: 01 Oct 2008
  • Loc: Upstate NY

Posted 27 March 2013 - 09:39 AM

I made up a small fly cutter that I use in a drill press or on the lathe, if you take light cuts you may be ok.


I'm following this as I have a few Celestron .965" visual backs I want to bore to 1.25. These should be easier as the existing bore is well centered and they are aluminum alloy. It seems to me tha flycutter should produce a better finish than a boring bit. Any opinions? Thx.

#13 Norm Meyer

Norm Meyer

    Mariner 2

  • *****
  • Posts: 252
  • Joined: 08 Feb 2009
  • Loc: Warren, ME 04864

Posted 27 March 2013 - 10:14 AM

George,
If you do the visual backs in a lathe mounted in a chuck
or on a face plate you would use a single point boring bar.
If you wanted to use a fly cutter the job would be done in
a drill press or milling machine. The fly cutter does not
automatically produce a better finish. The finish depends
on a number of things speed,feed, depth of cut, shape of tool bit, how rigidly piece is mounted. The way I would do
the job is in a lathe. The piece ,depending on its shape,size etc.
mounted in the chuck and a rigid boring bar in the tool post. That way I can control how much material to remove
by using the cross slide dials. If you have a 1-15/64 drill
and an 1.25" reamer you could drill and ream it, fast, easy and a good finish.

FWIW...Norm

#14 don clement

don clement

    Vendor (Clement Focuser)

  • -----
  • Vendors
  • Posts: 802
  • Joined: 02 Feb 2011
  • Loc: Running Springs, California

Posted 27 March 2013 - 11:08 AM

I made up a small fly cutter that I use in a drill press or on the lathe, if you take light cuts you may be ok.
fly cutter drawing


This type of flycutter is typically used for facing cuts on a mill. I use a boring head to precision bore holes on my mill such as the Flynn boring head shown below. A better type of tool to use on a less rigid lower powered drill press for boring a large hole would be a piloted trepanning tool such as Val-Cut. http://www.basstool....catalog/154.pdf I use an un-piloted Val-Cut trepanning tool on my small lathe to quickly bore large 2”-4” diameter holes followed by boring with a boring bar shown below.

Beware of boring holes in some cast iron such as bar bell weights, there can be very hard places if the cast iron was not cooled down properly when casting.

Don Clement

Posted Image

Posted Image

Posted Image

Posted Image


#15 StarStuff1

StarStuff1

    Soyuz

  • *****
  • Posts: 3870
  • Joined: 01 Apr 2007
  • Loc: South of the Mason-Dixon Line

Posted 27 March 2013 - 11:29 AM

I have only done this once, with a CW I machined to fit a Super Polaris mount. Years ago I obtained a drill bit set in 64ths inch diameter. Using one drill bit at a time with a floor mounted drill press did the job. Slow but sure and the work piece clamped securely all the time. It worked but I don't look forward to doing it again. Be careful.

#16 bykhed

bykhed

    Viking 1

  • *****
  • Posts: 792
  • Joined: 22 Oct 2007
  • Loc: Westminster, CO

Posted 27 March 2013 - 01:39 PM

Thanks everyone for the advice and thank you Norm for your kind offer. I think I'll try using a file or small sanding drum as I only need to increase the diameter a bit. This will be a LOT safer than risking the bit binding in the hole.

-Matt

#17 don clement

don clement

    Vendor (Clement Focuser)

  • -----
  • Vendors
  • Posts: 802
  • Joined: 02 Feb 2011
  • Loc: Running Springs, California

Posted 27 March 2013 - 06:25 PM

The last counterweight I made was brass not cast iron. Brass is easily machined in fact I threaded the counterweight with 2.5-8UN internal threads to match a 2.5” diameter threaded shaft. I modified the threaded brass counterweight with an aluminum insert for a CG5 mount the 20mm diameter smooth shaft shown below with the addition of a Turcite tipped thumbscrew to hold it in place. I prefer the threaded counterweight vs. a smooth shaft as the threaded CW makes it easier to balance. BTW the marks on the 20mm shaft were from the steel thumbscrew that came with the stock counterweight shown below the brass CW.

Don Clement

Posted Image

#18 bykhed

bykhed

    Viking 1

  • *****
  • Posts: 792
  • Joined: 22 Oct 2007
  • Loc: Westminster, CO

Posted 01 April 2013 - 03:02 PM

Update: Success! I took another look at the counterweight (I think it's an Edmund) and decided to try and drill it a tiny bit to see what would happen. The cast iron was actually pretty soft and I was able to bore the hole to 7/8" without any trouble. I ended up with a nice, smooth bore and a pile of iron filings. As a funny aside, the filings turn anything black and my hands were quite black when I finished. The counterweight now fits my Giro alt-az mount so I may correctly balance my portly Lomo Astele 150 Mak with a binoviewer.

#19 don clement

don clement

    Vendor (Clement Focuser)

  • -----
  • Vendors
  • Posts: 802
  • Joined: 02 Feb 2011
  • Loc: Running Springs, California

Posted 01 April 2013 - 03:21 PM

Good, you were lucky. If cast iron wasn't cooled too quickly when cast, then it is soft. Sometimes that isn't the case and extremely hard spots can form in cast iron which would have trashed your drill if made of HSS. I have had hard spots in cast iron even trash carbide tools. FYI cast iron chips and cast iron dust are abrasive and can quickly damage machine tools.

Don Clement

#20 Howie Glatter

Howie Glatter

    Vendor

  • -----
  • Vendors
  • Posts: 866
  • Joined: 04 Jul 2006

Posted 01 April 2013 - 04:15 PM

> As a funny aside, the filings turn anything black
>and my hands were quite black when I finished.

That's graphite, precipitated out of the metal when it solidifies. Hmm, I wonder if you could make something to mark on paper with it ?

#21 don clement

don clement

    Vendor (Clement Focuser)

  • -----
  • Vendors
  • Posts: 802
  • Joined: 02 Feb 2011
  • Loc: Running Springs, California

Posted 01 April 2013 - 05:10 PM

> That's graphite, precipitated out of the metal when it solidifies. Hmm, I wonder if you could make something to mark on paper with it ?


Isn't that lead? ;-)

Don Clement

#22 John Carruthers

John Carruthers

    Skiprat

  • *****
  • Posts: 3545
  • Joined: 02 Feb 2007
  • Loc: Kent, UK

Posted 08 April 2013 - 11:39 AM

...tastes like lead... :crazyeyes: :question:






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics