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endmill speed

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  • endmill speed

    I rebuild carburetors for antique tractors, and one mfg plugs the holes used to drill internal passages with what appear to be small ball bearings (0.140"). The balls are often recessed in the hole about 1/4". They have to be removed to clean the passages. After trying (and failing) with several types of end mills, I ordered a 9/64" carbide ball end mill, with a coating to "drill" them out. A couple of questions 1) I assume it may help to heat (the top of) the ball with a torch and let it cool first (?), and 2) what speed should I run my Bridgeport at when attempting to drill through the ball? The ball is probably C60 or so hardness before heating.
    Thanks much for your thoughts and insight!

  • #2
    IMHO you are not going to get anywhere if those balls are 60RC. I suspect you maybe dealing with a ball bearing. Yes it is possible to cut steels that are 60 RC but it is under very controlled conditions with very special tools. I would suggest you grind the ball out by rigging a die grinder on a mill and feed straight in try to make as large a hole as possible then use small chisel to chip away the rest. You may also try a drill made for hard materials. One trade name is hi-roc cant remember mfg. I still think you will have trouble. Most importantly don't use the endmill you discussed, it will be ruined.


    • #3
      C Tate is correct. Carbide tooling is meant to work on 45HRC and below. That "ball" is probably 68HRC.

      A diamond grinding pin may work. But a shop with a ram EDM will make quick work of those balls. If you can take a number of jobs to the shop at the same time, your cost will be much less.
      Barry Milton


      • #4
        As it looks unlikely that you can drillthrough the balls, how about going around them? A small hole saw with an ID slightly larger than the ball could be used to cut the metal away that surrounds the ball, letting it drop out. Afterwards, thread and replug the hole.

        All of the gear, no idea...


        • #5
          Just curious, 1)Do you know for fact the balls are hardened? 2)How do you prevent the ball from rotating while attempting to remove it? 3)Could the ball be rotating while attempting to cut it out? If it is, that will contribute to tool breakage. The EDM and grinding suggestions, IMO look to be the best options.
          Paying Attention Is Not That Expensive.


          • #6
            I have not seen an example of this so I am just guessing at a solution. It doesn't sound like there is anything that will keep the ball from spinning if you try to drill or mill.
            What is needed is a custom made tapered hollow punch that will slightly enlarge the hole opening to allow the ball to come loose.


            • #7
              I don't know who the mfg was, but some of those "old" carb bodies are cast zinc of aluminum. If you heat the ball enough to do any good (assuming it would), you'll most likely melt the surrounding body. (Zinc melts at around 800*F depending on alloy).

              I used to work at a carburetor mfg (Carter) back in the 70's as a designer. As you said, we used ball bearings to seal the external opening of cross drilled passages. They were plentiful, relatively cheap, had consistent sizes and worked great for the task.

              Ours were hardened. I suspect that some mfg might have used unhardened, but probably not. Would have cost too much to get something special and the unhardened might deform and not seal well. Sometimes the surrounding metal was "swedged or staked" to help keep the ball from falling out, but usually the hole was (At least the outside hole, sometimes there is a stepped passage. The interior passage might be .060 or smaller.) drilled to match the ball dia.

              Depending on the area where the ball is pressed in, you might be able to drill a small hole behind it and punch it out. Try to open the outer hole rim to help relieve the press on the ball.

              I'm guessing that your trying to blow out the passages with air and cleaner. I'd try drilling behind the ball, do the cleanout and then plug the new hole, leaving the original ball intact. It might not work in every instance. You might weaken some areas or drill into a critical area or it might interfere with some other function or part. Hard to guess without seeing the item. Alot of the passages are deep (1"-2" depending on carb model and function of passage, but some are real shallow. If you have enough knowledge on the particular carb (or detail drgs) you should be able to tell if you can bypass the original plug.

              Hope the above helps someway......




              • #8
                I think the ball would most definitely spin with the amount of pressure it would take to drill it out with carbide even if that was possible. Why not take an endmill slightly bigger than the ball and use it to counterbore down to the top of the ball. Then make a cutter out of round tool steel the diameter of the endmill, and grind a single point on it that could be used to bore around the ball, then slowly bore down until the ball comes loose. Also this tool would be held in a collet, not a boring head, so that it turns true with the hole made by the endmill. Make sure to relieve the center of the tool so that the tool doesn't make contact with the ball. Then just replug the hole when done.
                Jonathan P.


                • #9
                  Thanks for the numerous replies - lots of good info. The carbs were late ones built by Marvel Schebler and have cast iron bodies. I have used two methods to remove the balls. I drill a hole (#21 for 10-32 plug to tap/plug the hole when ball is out) down to the top of the ball, and use a wire-welder to weld a tail to the ball. Sometimes pulling on the wire pulls the ball out, often not. Persistence often pays off with this method. The second method is to drill down to the top of the ball, and then use a modified drill bit - (I converted the drill point to concave with a Dremel grinder to match the curvature of the ball), thus removing most of the metal around the ball. This, with the wire welder, usually works. If not, and the placement of the ball allows it, I drill a carefully placed hole at 90 deg to the ball and using a punch ground to a 45 deg angle "pop" the ball out.

                  I was looking for a more consistent, simpler method for doing this and spoke with a sales rep at Niagara Cutter - he thought a TiAIN coated carbide end mill might do the trick - particularly if the ball was headed red hot and allowed to cool a couple of times. The 9/64" end mill showed up a couple days ago and I was ready to give it a try, but neither the sales rep at Niagara nor my local tool rep who I bought it through could give me a suggested speed to run the end mill when "drilling" into the ball. From these posts I'm gathering this may not work either.

                  I was interested to learn from RPease that indeed the balls were ball bearings at Carter. MSchebler first used brass screws, then brass plugs, then lead plugs, then finally the blasted ball bearings to plug passages. Ian B suggested a small hole saw - I didn't realize they may be available that small (perhaps 0.150" OD) - can anyone confirm this? That would be similar to my "concave" drill bit, but allow me to go deeper around the ball. My modified drill bits require a lot of attention to keep them concave and cutting. And it sounds like japcas is suggesting the concave tool idea - which works but the edges of the drill are easily damaged. Apparently this cast iron has some hard places in it.

                  Again, many thanks for the suggestions and information. I learned a lot! I'll report back after I try the carbide end mill. I assume I should run it slow (200-300 rpm?).

                  Best Regards,
                  Duane Larson


                  • #10
                    I wouldn't want to speculate on speed, carbide usually likes fast. The 9/64" is small to use as a drill. Depending upon the material, LOC, and other factors, small dia. endmills have a tendancy to drift around when used in a drilling application. FWIW, I have never seen a hole saw smaller than 1/2".
                    Paying Attention Is Not That Expensive.


                    • #11
                      I would try a much faster speed and lots of cutting oil, I would also put some pressure on the quill lock to keep the endmill from jumping. I really dont think this is gonna be very succesful though, you will probably be lucky if the endmill doesn't break on the first one. I was gonna suggest the welding idea till I saw your last post. You might look into make a homebrew edm machine, I think some of the guys on here have made em or atleast can point you in the direction of where to find some plans. Good Luck


                      • #12
                        I have cut some tool steel with a carbide endmill like when needing to counterbore an existing hole deeper. It takes lots of rpms and no coolant and lots of pressure. The tool will get red hot but with the right amount of pressure it will begin to drill. The only problem is once you let up the endmill is usually toast. I doubt if you would ever get enough rpms on an endmill the size you will need to use to ever cut the ball bearing out. I still like the single point boring idea better though and the tool can be used over or resharpened using that method. Not nearly as expensive as trashing endmills.

                        [This message has been edited by japcas (edited 03-05-2005).]
                        Jonathan P.


                        • #13
                          Now that we know you are working in cast iron, I would say anneal the ball and go from there. You could use a torch, or salvage a carbon from an old flashlight battery and contour it to mate the exposed surface of the ball and hook your arc welder to it and anneal it that way. James


                          • #14
                            Any possibility of using hydraulics to remove the ball, a grease nipple adapted to fit the other end of the passage and just shoot the ball out the end?