If I am reading you correctly you are using a high speed "T" type parting blade. The only place for these blades is in a museum. The insert type (iscar or others) are so vastly superior it's hard to believe. I remember the old days of parting with those old blades, and squinting and tensing up, just waiting for the inivitable moment that the blade would grab and either break or tear the workpiece out of the machine. Years ago my brother worked third shift (alone) parting 3" bar on a lathe with the new insert style tools. Just for fun he kept increasing the infeed one step at a time,just to see the limit of the tools ability. He was very surprised how fast he could plow through before the tool broke.He insisted on me changing to the insert system and I feel it was one of the best upgrades I have ever seen.
Hmmmm........I wonder how they ever parted items then before the advent of insert tooling? I have never used a T shape parting tool but use the typical sort of V shaped parting tool in HSS as well as insert type all the itme......I sure would not like my HSS parting tools to get put in a museum, as I use em too much.
If the high end of the angle wa to the right, the finished part that was dropped should be relatively free of a nib. Sometimes it helps to grind the sides (both sides) of parting tool blade so they have a long taper, not much but some so as the parting tool is entering the work the sides are free adn clear from the cutting edge back. A small nick or V ground in the very end of the cutting tools working edge will also help to some degree to curl up the material as its removed. Lots of lube certainly helps, for keeping it cool and friction free. I find power feed to be a much better method than trying to free hand it which a lot of folks do since they are a bit nerveous on powerfeed parting. Usually on a lot of stock you may even have to change feeds and speeds 2 or three times until its parted off. Its also importasnt that the parting tool is 90 deg to stock being parted.
============================================== Put some color in your cheeks...garden naked! "The original frugal ponder" ~~~~ } ~~~~~~ } ~~~~~~~ }
How deep a cut can an insert make into material? I am using a "T" type for cutting wood dowels in a metal lathe that are some times 1.5" in diameter and I thought you could only cut about a .5" with an insert. Dick
I didn't say the hs blades didn't work, just that I have never seen such an improvment in any other tooling system, probably due to the unusual geometry of the top face of the carbide parting insert type. I also wondered how they used to move heavy objects before the wheel was invented!
======================================= Cutting off [or parting off for our GB readers] is one of the more arcane and black-art aspects of lathe machining. First about the angle grind. This was ground at an angle so the the cut-off pip or tit would be to the left. While this may be a "good thing" for high volume production I find that it causes problems for for two reasons: (1) it is difficult to get the c/o tool set exactly on center and (2) it generates a chip that is wider than the width of the groove, which can be a major source of problems.
Plain c/o tool blanks are a major PITA [at least for me] and I have had much better results with the "T" style cutoff with a radius in the top of the "T" as this tend to produce a chip that curls in on itself thus is slightly less in width than the slot allowing easier exit.
I suggest grinding the tool straight across with about a 5 degree [effective] front clearance angle. The side clearance angles are set by the shape of the tool blank. Because of the "dish" at the top of the "T" there is a few degrees of effective side rake or hook which seems to help a great deal.
A suitable holder will make a huge difference in performance. I suggest a holder with 3 to 5 degrees of back rake. This will require that you increase the measured front clearence by this amount to get the suggested 5 degrees clearance.
As I indicated before the tool must be set to be exactly on center and exactly at right angles to the axis of ther part. I find it is wothwhile to keep a new "dead center" with a sharp point just for use as a reference for setting the tool height.
A critical area which most people do not consider is the increase in width of the c/o tool with heat. In normal turning this does not cause a problem, but because of the c/o tool is cutting in a deep slot and bounded on both sides, any appreciable increase in heat and thus tool width will cause problems. A continuous stream of lubricant/coolant is a necessity, both to keep the tool cool and to flush out the chips. I find that for home use a "windex" type spray bottle that can be adjusted to shoot a stream is very handy. While you can use regular black sulphur [or other heavy duty] cutting oil [try cutting with paint (not lacquer) thinner [aka varsol] if too this is too thick], I find that water soluable seems to work better in this application, most likely because of its better cooling action. If you want to avoid buying a 55 gallon drum you can get "water pump lubricant" at most car parts stores/counters which is the same thing. This will leave an oily protective film when the water evaporates. One tip -- if you have hard water in your area use distilled. This will help avoid the scum/deposit that hard water causes with water soluable coolant.
One of the best things I have found to improve cutting off (in addition to using the 'T" style cutter) is to fabricate an "upside-down" tool holder which mounts at the rear of the cross slide which incorporates 3 to 5 degrees of back-rake. The chips clear the groove much better and the rigidity of the operation, which is always important, seems much better.
You can see pictures of this at
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this tool holder and a T-15 blade we have "parted off" 1.5 inch diameter pre-hardened [stress-proof] shafting with no difficulty [but a large amount of "pucker"]. If it would be helpful I will send you a dwg [autocad] file of this tool holder sized to fit an Emco compact 10. The location of the slot for the c/o blade must be adjusted for the center height of your lathe and the desired amount of backrake. In our case a maximum blade extension of 1_1/8 inches was used, allowing up to a 1 inch depth of cut or a 2 inch solid bar.
You also need to remember that cutting off involves a thin tool with a large amount of overhang which causes problems by itself.
Feeds and speeds are another thread. The heavier the feed the thicker the chip and the more heat that is generated. The faster the speed the more heat that is generated. With the upside down holder and T-15 blades I have found that the highside RPM that you would use for regular HS machining for the material and diameter seems to provide a good starting point. Note that for a given rpm the effective sfm will be the highest at the start of the cut and decrease to zero at the exact center. The Emco Compact 10 has only manual cross slide feed, but the general rule seems to be to not let the tool rub as this cause heat, but to keep the feed to the low side to produce thin chips and low heat. [Stainless that workhardens is another topic] You should back off the tool frequently to make sure the chips are clearing and to allow the tool to cool down. Unless you are in a production environment, the few minutes you save by maximizing the c/o process are not worth the aggrivation.
While we used T-15 cutoff tools, this was because we received several of these in some donated tooling from a screw machine shop. Regular M2 seems to work as well for low volume usage and has the benefit that it is easier to grind, is less brittle that cobalt or carbide and thus less prone to corner chipping and breakage. OBTW -- watch for corner wear and chipping/breakage when parting off and sharpen the tool as soon as you notice this or you notice that the machine seems to sound different or seems to be working harder. It is *MUCH* quicker/cheaper to touch-up the end of the tool and reset it than it is to correct a "crash" which may involve a new tool and a scrapped part. Corner damage is prone to occur at the start of the cut both because of eccentric part location -- the tool digs in and because of surface contamination -- rust. If you are using salvage materials be careful of case hardened shafting.
The purpose for that is so it parts the workpiece off from the stock with a minimum "tit" left. Then, the remaining part of the parting tool finishes facing the stock still in the spindle.
The disadvantage of this angle is that if there is a lot of extension of tool (e.e. for a deep parting), the HSS tool can bend a bit, resulting in an end which is concave on the workpiece, and convex on the stock. But this can depend on what material you are machining.
I get the wide chip part. The tool had a very steep angle by my thingking likely 30 degrees or more.
I want to make sure I understand plain vs T. The HSS blank is wider at top for about an 1/8's or so of an inch and the rest of the blank is narrower. Is the plain a rectangular profile?
I didn't notice the dish but I will look tomorrow when I get to work.
Thanks for that tip.
Our cnc's use water soluable. I was using sulfur oil with a brush.
Please send file. My anti spam address is at bottom. My other address also works but I don't check that one also.
I saw the pictures on your site. The gent milling should have had safety glasses on.
========== You are correct, however in that picture Chris was not machining but using a magnetic sine bar and a test indicator to get vise adjusted to exactly 4 degrees for the back rake. This was another instance where the set-up took longer than making the cut. Students got a good review in [and in some cases introduction to] trig to get everything laid out and the vise set for 4 degrees.
My ISP is having problems with outgoing emails at the moment, but as soon as they get the problems fixed I will send the drawing in acad200f dwg format to you. As indicated in the cover email I can save in most any acad dwg/dxf/dwf format if the 2004 dwg format is a problem.
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