Cutting threads

[jgross]

I'm consistently having problems cutting threads. We have a HAAS toolroom lathe and are running X4. Using the default settings and even adjusting the minor dia. allowance more than the tables call for the threads never cut deep enough. I've fudged it by increasing the tool radius and/or altering the minor dia. with mixed results, but it seems I should be able to cut some threads without having to guess at the parameters. Any one else have this problem or have any suggestions?

[htm01]

we have a SL30 and toolroom and the guys complain about the same thing and have to go deeper

[jgross]

What is the best method you've found? I've had mixed results using WEAR settings on the controller or increasing the tool radius to make it cut deeper, but it's also a pain in the #@% to change parameters in Mastercam and always have to repost.

[3R!< W3NG3R]

we don't have that problem.

 

For normal threads, the prog works fine.

For fussy threads, tool comp is what we use to tweak it in at the machine.

[Mike@Dive Lab Inc.]

Ive always had the same problem and never figured out what going on

[Mike@Dive Lab Inc.]

I contacted HAAS so we'll see if they can shed some light on the issue. The minor in the program is correct, but the threads arent close to the proper depth. As soon as I hear something I'll let ya know.

[jgross]

Thanks Mike. I'll be waiting with baited breath. We don't use our lathe all that much but it's a problem we just haven't been able to resolve.

Let's hope HAAS has an answer!

[hugh jars]

We also have the same problem on manual and cnc, internal and external threads, and as yet I don't know why. Sometimes we solve the problem by adjusting wear offset, sometimes by tool geometry offset and sometimes by programming so it's total confusion.

 

I wonder if the problem is due to the rounding of the insert being of a smaller radius, or truncation being less, than that used in the threads in the tables (my tables were probably compiled in the 1960s). If that were the case then when you got a touch-off position, the insert flanks would be further from the surface than anticipated. It's got me thinking - I'll see if the insert manufacturers have their own set of tables for threading depths.

[Scott Lundin Shopware Inc.]

The thread depth calculations will never be dead on. An insert from tool company A has a different radius on the tip than an insert from company B. Most general threading inserts have a tip radius that is much more pointed than in needs to be. This is so it can do more than one pitch thread. If you use a crest topping insert for a specific pitch thread, you will notice that you won't have to offest the tool on the machine quite as much as a general thread insert. This is because the tip radius is the proper size for that particular thread pitch. A general thred insert will probably need around -,010 to -.012 offset at the machine control for an OD thread. Been that way since I started with CNC machines in 1975. Also thread inserts have a manufacturing mold tolerance of plus or minus .003 inch. This aslo causes inaccuracies in the thread height. Thats why lathes have X offsets, use em.

[Mike@Dive Lab Inc.]

I've tried full and partial profile inserts with the same results. I figured it may have something to do with the R. of the tip and geo of the insert. Just not sure

[Paul Murdock]

If you're using a partial thread insert you need to modify the results that master will input as the thread depth.

 

Example - you have a 8-48 partial profile insert. The radius on the end is going to be for 48 tpi. So you're going to have to adjust your depth. Height of thread is = .866*{1/tpi}. If external thread then radius is 1/4 of overall height. So you need to go deeper by the calculated amount of 1/4. I'm on my cell right now but if you would like a clearer explanation I can write it up. I always had trouble matching thread until I figured this out.

 

Cheers!

Paul

[jgross]

Paul, if I understand you correctly your talking about the lay down profile inserts that cut a specific thread profile. I'm using a standard 60 degree insert for UN/UNC threads. A very minimal radius (.005-.010 max). I set the minor dia. in Mastercam, I even fudge more than the actual minor dia. Shouldn't it cut to those depths? I have even lied about the radius at the machine to make it cut deeper with sketchy results.