jackie schmidt
New member
One of these days Gunsmithing will get out of the stone ages.........jackie
Cut off tooling??
- Thread starter skeetlee
- Start date
Probably not
It still comes down to money. It's pretty hard to find a profit in tiny custom jobs.....figure out how many rifle barrels you'd have to fit in a month to just cover your company payroll! I'm trying to make the numbers work for building on spec and even then, running flatout hoping to sell out it's a pretty hard pull.
al
One of the biggest mistakes I see people make is not indicating the cut off blade straight. If it is on an angle it WILL bind & snap. The other 2 important things are being dead on center or a few thou below & keeping cutting fluid on the tool. Advancing the compound forward until it runs out of travel & removes play also helps with rigidity & flexing.
JerrySharrett
Senile Member
There is no comparison between the SB 13 and many of these modern ChiCom imports, The SB 13 is more rigid than the SB H10 which is ten times more solid than the ChiComs.
I'm afraid that trying the method of high rpm on a ChiCom might get someone hurt really bad. Why? Chatter! The SB with sleeve bearings will not chatter and chatter is what kills the carbide tipped cutoff tools. Jackies P&W is a rigid, heavy duty cycle, job-shop lathe built to do heavy machining and last for years, just like the SB.
As they say "do not try this at home"!!!
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Wayne Shaw
Active member
The most used power tool I have is a "port-a-band" saw. I hate hacksaws and the only thing I use a parting tool on is aluminum.
M
mike in co
Guest
simple way to get the tool straight is to put the side of the blade on the face of your chuck.....and get it square there.....
mike in co
mike in co
C
Chip Soles
Guest
It can be a B****. The hss blades are a bomb looking for a fool waiting to pick it up. When that was the only way, you bought them by the dozens. Yes, inverting the blade to allow the cutting process to be reversed does really work quite well. I have parted off 6" dia. rounds this way. Why does it work? Don't know, but it does. It is not even close to what can be done with the likes of Iscar, and others that a chip forming carbide. The depression in the top face of the insert forms the chip to have a varied cross section which causes the chip to narrow, and eliminate friction between the chip and the groove. Now to the subject of feeds and speeds. Consult various sites, as to grades and coatings that match your applications, as well as the recommendations of surface speeds RPM= (4*CS)/DIA. Then increase the feed rate to get the chips to break as "c's" I prefer to place the coolant or oil on the back side of the groove to allow it to make the bottom of the groove. On large dia. pieces, you may need to increase the RPM as the dia. and the surface speed decrease together.
DO NOT stand in front of the groove to watch the show!! That is where the fecal material will come from the fan.
Regards,
Bob
Regards,
DO NOT stand in front of the groove to watch the show!! That is where the fecal material will come from the fan.
Regards,
Bob
Regards,
I would imagine that the reason cutting upsidedowney helps is because cutting conventionally you're lifting the chuck, unloading the bearings.
al
MilGunsmith
Member
I have been grinding a chip forming groove in the top of my HSS cutoff tools for years. Use a dremel bit and make it look like the carbide inserts.
4
4Mesh
Guest
No Al,
I think you'll find it's the chips caught in the groove that kill the tools. Doing it upside down makes gravity help with getting rid of the chips.
J
J. Pendergraft
Guest
Bill,
Your comments are dead on with my experiences. Plenty of cutting fluid, and I back out the moment I see the chips start to build up in the groove. If the groove is deep it progessively gets harder to complete the cutoff. Sometimes on a deep cutoff I will stop and widen the kerk some towards the O.D. to allow easier escape of the chips. I have busted a few tools and they are expensive so I do my best to avoid breaking stuff.
Joel
I'll buy that..... my guess was for those who're experiencing chatter, 'climbing' and blowing bits. I've never had the jamming thing happen to me because all my cutoff bits and blades are HSS set to make curls instead of chips. I learned to cutoff while monitoring my curl.
al
jackie schmidt
New member
As for the cutting upside down thing, we do quite a bit of "upside down" machining.
Especially when boring with quite a bit of bar overhang. In fact, when machining large bronze bushings, that could be as long as 20 inches, the usual procedure is to put the tool on the backside, upside down. Of course, the bars we use on a bushing this size is 5 inches in diameter.
The main advantage is it keeps the bar from digging in when it trys to flex. I think it is the same theory that says it is easier to pull something than to push it.
Experienced Machinist learn all sorts of tricks that allows one to make the most of the tooling on hand. It's all in a days work.
A couple of years ago, I posted some pics of a outside boring job where I bored some huge Dredge Boat Stantions that were 45 inches in diameter. I did the job with out 4 inch portable boring bar. It took some rather creative thinking on the set-up, but it goes to show what you can do with a little thought...........jackie
Especially when boring with quite a bit of bar overhang. In fact, when machining large bronze bushings, that could be as long as 20 inches, the usual procedure is to put the tool on the backside, upside down. Of course, the bars we use on a bushing this size is 5 inches in diameter.
The main advantage is it keeps the bar from digging in when it trys to flex. I think it is the same theory that says it is easier to pull something than to push it.
Experienced Machinist learn all sorts of tricks that allows one to make the most of the tooling on hand. It's all in a days work.
A couple of years ago, I posted some pics of a outside boring job where I bored some huge Dredge Boat Stantions that were 45 inches in diameter. I did the job with out 4 inch portable boring bar. It took some rather creative thinking on the set-up, but it goes to show what you can do with a little thought...........jackie
I can't see how the workpiece or the bit sees "pushing" or "pulling" differently in the setup you describe. IMO backside and upside down = frontside and rightside up...........except for the reaction of the hs bearings.
Parting off stock..
Parting requires patients and tooling properly aligned both vertically and horizontally run at the correct feed and speed for the tooling and material being parted. Coolant and swarf removal are crutial to tool life.
In looking at this post and knowing it is on a Gunsmith thread I will make the following comment.
I never part off gun barrels with a parting tool. I cut them with a band saw. The reason parting induces stress into the surrounding areas either side of the part. If one looks at the grain structure of a gun barrel before parting and again after parting one will find a parting tool effects the metal for about an inch on either side of the part. A band saw on the other hand stresses the metal about .250 on either side of the cut. I cut with a saw then face off approximately .250. I run the tool point straight in or away from the bore. Folks here may not agree, but that is the way I was tought and it has served me well over the years. Stress and accurate barrels are not normally found in the same place.
Nat Lambeth
Parting requires patients and tooling properly aligned both vertically and horizontally run at the correct feed and speed for the tooling and material being parted. Coolant and swarf removal are crutial to tool life.
In looking at this post and knowing it is on a Gunsmith thread I will make the following comment.
I never part off gun barrels with a parting tool. I cut them with a band saw. The reason parting induces stress into the surrounding areas either side of the part. If one looks at the grain structure of a gun barrel before parting and again after parting one will find a parting tool effects the metal for about an inch on either side of the part. A band saw on the other hand stresses the metal about .250 on either side of the cut. I cut with a saw then face off approximately .250. I run the tool point straight in or away from the bore. Folks here may not agree, but that is the way I was tought and it has served me well over the years. Stress and accurate barrels are not normally found in the same place.
Nat Lambeth
C
Chip Soles
Guest
A lot of the chatter that occurs during parting off a piece, is due to the tool geometry, excessive overhang, worn way surfaces, loose gibs, and improper speed and feed settings. With more experience in parting 5-6" dia. 34Rc 420 SS than I really wanted, Some of the best improvements to a bad job were the developement of the chip forming carbide inserts with coatings which allow higher speeds, and enough chip load to load the insert, and not allow it to out cut the feed, which can start chatter. The other improvement in my mind anyway, are the various ridgid tool post configurations. The ridgid toolpost with interchangeable holders alows the post to be squared, and the various holders, with proper geometry can be ready to go. In parting off parts, size does matter, and this is where a long tool will get you into trouble. When parting larger dias., extend the blade to allow a partial cut. Then extend the blade, and increase the rpm to suit the smaller dia. on the next part of the cut..... Another thing that may help to reduce the chatter is to set the compound rest parallel to the bed ways. This should put the cutting forces against the long way surface, rather than the feed screw/nut.
Regards,
Bob
Regards,
Bob
lejarretnoir
JP Poulin
Some good tips there Chip.
I watched a CNC lathe on youtube [can't remember which one] where the RPM's increased as the tool worked it's way to the center. The feed stayed the same.
On a Broughton I recently installed, it actually said to not part the barrel, but bandsaw cut instead. I've noticed the amount of heat when parting and realized how important coolant is.
I watched a CNC lathe on youtube [can't remember which one] where the RPM's increased as the tool worked it's way to the center. The feed stayed the same.
On a Broughton I recently installed, it actually said to not part the barrel, but bandsaw cut instead. I've noticed the amount of heat when parting and realized how important coolant is.
jackie schmidt
New member
Al, all I can say is it works......jackie
AMMASHOOTA
Gary Gruber
not wanting to be contentious, but it was Al Gore's father that invented the lathe. His grandfather invented electricity, but another dude was given credit for it. while he may not want to admit it for fear of having his citizenship questioned, if you examine the Gore family tree, it was actually direct descendant's of Adam Gore who built the pyramids.
Lee I was once told by a used machinery dealer to fill the base of my old lathe with concrete........I haven't done it yet but have come across a couple of peole who did that in the past and both said the lathe was much better to use afterwards.........Ian