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How to complete this part??

Discussion in 'A BEGINNER'S FORUM (Learn How To Machine Here!)' started by WesPete66, Jul 7, 2017.

  1. WesPete66

    WesPete66 United States Active User Active Member

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    I am in process of making a part & could use some pointers.. (Lathe is an Atlas QC54. Am using HSS tooling)
    The part is a ring, 2.25 OD x .75 ID x 1.00" long/thick. On one side is a recess, or counterbore, of 1.625 dia x .875" deep. What would be your choice of HSS cutting tool and process to make this recess? I've looked at some youtube videos & haven't found much in common amongst them. Help please?
    Thanks!
     
  2. kd4gij

    kd4gij United States Active User Active Member

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    I would use a boring bar.
     
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  3. pdentrem

    pdentrem Active User Active Member

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    Lantern tool post or QCTP?
    Pierre
     
  4. mikey

    mikey Active User H-M Supporter-Premium

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    I agree.
     
  5. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    A counter bore is one of the most common operations that you will ever do in lathe work.
    Face it and bore it with a boring bar that will fit into the hole that is extended just enough to clear the holder, having not mentioned the material no other parameters may be suggested. At 7/8" deep this far less then one diameter so hit it hard.
     
  6. WesPete66

    WesPete66 United States Active User Active Member

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    Sorry, yes on the QCTP, and the part is steel (CF from the local welding shop).
    But how does one make a boring bar create a flat bottom recess? I'm picturing a boring bar with a .250 square tool bit in a hole, held in with a set screw.. Do you just extend that tool bit out long enough to cut to the full depth needed, while the end of the bar protrudes through the thru-hole?
     
  7. ddickey

    ddickey United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Are you wanting to grind your own tool?
    If so this vid may help
     
  8. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    Having not used such a tool in 30+ years I now see why the question was asked. If you insist on HSS tooling buy a solid bar for such a small hole or a bar that holds square or round bits at an angle like so. Cumbersome for small holes however
    https://i.ytimg.com/vi/chiJb7Xp2rk/maxresdefault.jpg
     
  9. Silverbullet

    Silverbullet Active Member Active Member

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    Many of the older style boring bars have two ends one is straight a cross the bar the other end at 45 degrees to the bar. With that they make it easy to use high speed tools ground to perform the operation. For the bore your doing a self ground bit an extra long tool bit would do.
     
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  10. mikey

    mikey Active User H-M Supporter-Premium

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    Okay, I think I might have a simple solution involving a simple HSS tool you can grind quickly. Its called a knife tool and looks like this:

    IMG_4533.jpg

    I am assuming you are familiar with tool grinding and will give you simple angles. If you need more info then please let me know so I can clarify. This tool has a side cutting edge angle of zero, side relief of about 15 degrees, an edge cutting edge angle of about 70 degrees with 15 degrees of end relief. It has a side rake angle of 15 degrees and a back rake angle of 10-12 degrees. The nose radius is less than 1/64"; small but it is there.

    You already have a 0.75" ID hole, correct? If you mount this tool so that the shank of the tool parallels the ways, you can just touch off at the surface, move the tip into the center bore, dial in your desired depth of cut and feed out with your cross feed to cut outward. It will allow you to precisely size the counterbore very quickly.

    Let me know if this is unclear. I could probably have cut the counterbore in the time it took to type this.
     
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  11. WesPete66

    WesPete66 United States Active User Active Member

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    Ok so looking at what's available for basic boring bars, and finding the sets of small bars with carbide tips. Is a carbide tool a good choice for an Atlas lathe with QCTP? I keep reading that carbide is not good on basic hobby lathes. ??
     
  12. Jonathans

    Jonathans United States Professional Fish Killer H-M Supporter-Premium

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    I used to use carbide cutters all the time on my Southbend 9" lathe with a QCTP with no problems at all.
     
  13. mikey

    mikey Active User H-M Supporter-Premium

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    I assume you're referring to those 9 piece Chinese brazed carbide boring bar sets you can get for about $10.00 or so. These will work fine for your job since you're not going very deep. Like all brazed carbide tools, they are not very sharp out of the box so use your diamond stone to hone it to a sharp edge. I like a very tiny nose radius on mine to improve the finish. Most of these tools have a zero-lead so they are not ideal for closed bottom bores but for a counterbore, they will be fine.

    Boring is not the same as external turning. The cutting forces are the same but in the case of boring, the bar is what deflects the most. Accordingly, use the shortest bar with the biggest diameter that will fit in the bore and you should be fine.

    You will find that a small lathe will bore just as accurately as a larger lathe. The issue you face is cutting speed. Unlike a carbide insert, the cutting speeds for a brazed carbide tool is not published so it comes down to experience. I actually used these bars on my Sherline lathe to bore all sorts of stuff and while they are not the most accurate bars, they get the job done. I run them at the top speed my lathe will achieve, about 2800 rpm and have had good results. I rough at about a 0.020" deep depth of cut and feed to get as curled chip as I can get. I finish with a 0.005" depth of cut and this works well for me.

    What you need to do is take a spare work piece and figure out what the change will be in inside diameter for a given depth of cut. The most important sample cut will be a finish cut. Say you dialed in a 0.005" depth of cut and it produced a 0.009" change in ID. Knowing this, you can rough until you hit 0.018" ID and then dial in your 0.005" cut and measure again. If it consistently produced a 0.009" change in ID, dial in another 0.005" and you should come in on size. If it didn't give you what you expected then change your final depth of cut.

    You would do the above regardless of the kind of bar you use - inserts, solid bars or brazed bars. The trick is to know how your bar cuts for the given set up you have on that job. Remember that coolant makes a big difference in the chip form, finish and how the bar cuts. A bar will cut one ID without coolant and another ID with coolant so experiment and try. Also, if the bore has to be accurate, let the part cool to ambient temp before taking your measurement before that final pass or two.
     
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  14. pdentrem

    pdentrem Active User Active Member

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    I used either a boring bar or a chipped carbide end mill.
    Pierre
     
  15. machPete99

    machPete99 United States Active Member Active Member

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    Search for "everede boring bar" on ebay etc. They are very nice for doing this sort of work. The ones I have use a small triangular cross section piece of HSS or Carbide to do the cutting. To do a counterbore you need one with some angle to provide clearance for the holder.
     
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