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View Full Version : jigs and carbide vs HSS/cobalt



M.Grimes
10-12-2012, 03:35 PM
:confused::confused:I thought I would throw this out and get opinions,first , I use carbide lathe tools mainly because I am lousey at grinding tools .Any body out there have:confused: any pictures of jigs for grinding turning and thread cutting tools.Second any opinions on carbide vs HSS/cobalt for general use.Carbide tools are convient but expensive.I can get HSS/10% cobalt lots cheeper.I just need to get some Ideas about making a jig to grind and resharpen tools.Thanks.

willmac
10-12-2012, 05:44 PM
I use both carbide and HSS tools. The main reason for the carbide tools is that I can use higher speeds, and this is helpful for some jobs. As far as grinding HSS lathe tools is concerned I don't use jigs. Most lathe tools just need clean sharp edges at roughly the right angles. You can achieve this by hand and eye alone with the occasional help of a simple protractor. Screw cutting tools do need to be more accurately ground than this, but even then you can manage without jigs, just careful use of a protractor. You don't even need to use the rests on the grinder, in fact I find easier not to. Just get a decent set of wheels on your grinder, dress them properly and get some practice in. Don't use HSS for practice; a bit of mild steel will do perfectly well for getting the hang of it.

J. R. Williams
10-12-2012, 06:09 PM
If you are going to use and grind carbide, invest in a good diamond grinding wheel.

RussZHC
10-12-2012, 06:12 PM
Willmac is right on...my jigs are in limbo as I have found the more I grind the "easier" it gets esp after using and the more you use the more variations you will find you need and the more you grind the easier it will likely get.
I still want to make some simple jigs due to being able to repeat an already ground angle (touch ups etc.) and they certainly will help but are not a neccessity

This http://bbs.homeshopmachinist.net/threads/35818-Grinding-Lathe-tool-Bits?highlight=grinding+lathe+tool+bits is a pretty good thread. You will be able to find others, read them through though since sometimes early postings and the ideas in them change or get modified.
Find the tubalcain/Mr Pete videos, I think there are 2 or 3 dealing specifically with grinding lathe tool bits, he uses large models that give a very good idea of angle basics.

Welcome to the bbs by the way.

I found I am beginning to use carbide inserts a bit more as the speed/DOC aspects seem to help deal with the mystery metal I use most often. At the same time I have also found what an insert can do in terms of finish and then grind a HSS tool looking for the same end result.
Edit to add: be aware that not all HSS is the same, small amounts of various additives can make a lot of difference...it is not that most all is not useful more that there is a difference and even HSS can get expensive

Boucher
10-12-2012, 10:27 PM
This is a setup to grind threading tools using a HSS parting blade. The basic shape is roughed out on the grinder then the 60 point is refined using the compound on the lathe. The wheel in the chuck is a CBN.
http://i109.photobucket.com/albums/n50/boucherbyron/IMG_0267Small.jpg


This is a guide made using HDPE. The table is tilted 7 to establish the relief.
http://i109.photobucket.com/albums/n50/boucherbyron/IMG_0073.jpg

Here is another made using Delrin. This type is made to fit the particular size tool bit. The previous one will work with any size bit.
http://i109.photobucket.com/albums/n50/boucherbyron/IMG_0074.jpg

oldtiffie
10-13-2012, 02:40 AM
I use both carbide and HSS tools. The main reason for the carbide tools is that I can use higher speeds, and this is helpful for some jobs. As far as grinding HSS lathe tools is concerned I don't use jigs. Most lathe tools just need clean sharp edges at roughly the right angles. You can achieve this by hand and eye alone with the occasional help of a simple protractor. Screw cutting tools do need to be more accurately ground than this, but even then you can manage without jigs, just careful use of a protractor. You don't even need to use the rests on the grinder, in fact I find easier not to. Just get a decent set of wheels on your grinder, dress them properly and get some practice in. Don't use HSS for practice; a bit of mild steel will do perfectly well for getting the hang of it.

+1

A "spot on" reply Bill.

If they get hand-grinding of drills they will be off and running.

Marking out and centre-punching is next.

They are are all "manual" (only) skills that need to be learned and practiced regularly.

Rosco-P
10-13-2012, 07:44 AM
I use both carbide and HSS tools. The main reason for the carbide tools is that I can use higher speeds, and this is helpful for some jobs. As far as grinding HSS lathe tools is concerned I don't use jigs. Most lathe tools just need clean sharp edges at roughly the right angles. You can achieve this by hand and eye alone with the occasional help of a simple protractor. Screw cutting tools do need to be more accurately ground than this, but even then you can manage without jigs, just careful use of a protractor. You don't even need to use the rests on the grinder, in fact I find easier not to. Just get a decent set of wheels on your grinder, dress them properly and get some practice in. Don't use HSS for practice; a bit of mild steel will do perfectly well for getting the hang of it.

Another +1 one to the above.

Learn to freehand grind your HSS tools as has been said here a million time before. Practice on some scrap square stock. Hone the edge when your done. Learn to put a small nose radius on the tool. You don't need a precision jig and a surface grinder.

SGW
10-13-2012, 08:10 AM
If you're really into grinding lathe toolbits, see if you can find a copy of "The Design and Use of Cutting Tools" by Leo St.Clair. It's a 350+ page treatise on single point toolbits.

He makes a few basic points:

The angles do matter, both in terms of cutting efficiency and tool longevity. When he tested an assortment of machinists for their ability to freehand grind, say, a 7 degree cutting angle, he found that nearly all of them were way off. If grinding freehand, he recommended getting one of those small swing-arm protractors and measuring what you grind.

A guide of some kind lets you accurately grind the same angle you ground last time, so you end up grinding less when you resharpen.

A guide doesn't need to be fancy. StClair recommends using just a flat horizontal table, adjustable in height, in front of the grinding wheel. Depending on how high the table is above the grinding wheel centerline, a line tangent to the o.d. of the wheel will form a certain angle with the horizontal plane of the table. Set the table at whatever height you need to achieve the angle you want, and just put the toolbit flat on the table and slide it against the wheel. The edge will come out slightly hollow ground, which St. Clair claims is a good thing.

So that's what I do. But can you grind a perfectly workable toolbit freehand? Sure.

J Tiers
10-13-2012, 10:22 AM
let me say that the idea that you can grind good bits by hand is correct.

BUT............

if you want to just get on with work, and not futz around, why would you NOT create a jig for grinding form tools such as threading, etc? It's going to be a repeat job, you WILL be doing it again. Other than for "poking the newbie's head into it", similar to the "file this lump to a perfect 1" cube, kid" deal, there isn't any good reason to always hand grind a form tool.

By all means create a jig for any repeat grinding job, and enjoy the benefits.

Forestgnome
10-13-2012, 11:49 AM
The Workshop Practice #3 book called Screwcutting in a Lathe has some great examples of grinding tools for cutting threads along with plans for a jig. Plus you get valuable info on screwcutting. Cheap.

bborr01
10-13-2012, 12:15 PM
If you are going to use and grind carbide, invest in a good diamond grinding wheel.

And a good dust collection system.

Brian

ldbent
10-13-2012, 03:18 PM
I bought six-three quarter inch shank-sixty degree threading tools on ebay for a dollar a piece. I have HSS dies for common sizes of one half inch or less. I see no point in making ten cutting passes when it can be done in one.

Evan
10-13-2012, 03:55 PM
I hand grind everything including regrinding carbide and even cermet tooling. I have even reground diamond inserts since diamond can be ground with diamond (slowly). I learned hand grinding in the aircraft industry where you had the option of a 15 minute trip to the tool crib or a 2 minute trip to the grinder on the floor. The lead hand gets pissy if you take too long. As said, learn to grind drill bit and the rest follows.

Also, tungsten carbide dust is toxic and if inhaled causes "hard metal disease" which you do not want. Wear a dust respirator when grinding carbide.

lane
10-13-2012, 08:51 PM
Go here
http://shopswarf.orconhosting.net.nz/turntool.html

Forrest Addy
10-13-2012, 09:40 PM
Hold your nose an buy one of these. Toss the green silicon carbide wheel that come with it. Seriously, the green wheels will wear down carbide and put something like an edge on it but they are nearly useless on HSS and they generate clouds of dust. I won't have them in my shop because of their low utility and the dust problem. Replace the green wheels with an aluminum oxide wheel and a diamond wheel.

Here's the Enco version of the famous Baldor (and predecessors) 6" face wheel grinder:

http://www.use-enco.com/CGI/INSRIT?PMAKA=891-8106

The virtue of this Baldor clone is it's cheap and its wide platen, miter gages, and adjustable tilts make your settings quick and accurate. There are many of these grinders on the import market all made by the same people possibly but the prices are all over the map. I've seen them on sale at Harbor Freight for $159. BTW be sure you get a face wheel grinder with a reverse switch. Some tools are better ground on the right side of the wheel and you don't want the swarf in your face or the wheel trying to lift your work off the table..

The plate mounted alum oxide wheel (Shape designation: type 50) is available from MSC for $50 or so.

MSC part: 90852377

Use the diamond wheel for carbide only. HSS will rapidly use it up. (carbon dissolves in iron) Most any diamond wheel that fits the backing plate will do. The shape designation is "6A2".. I suggest this bottom of the line wheel from Shars (Discount Machine).

http://www.ebay.com/itm/6x3-4-DIAMOND-PLAIN-CUP-WHEEL-GRINDING-D6A2C-150-GRIT-NEW-/300606281721?pt=LH_DefaultDomain_0&hash=item45fd87d7f9#ht_2430wt_646

This is an expensive remedy but the face wheels and the setting quadrants make repeatable tool grinding a certainty. If you know the angle you need you can grind them on this rig.

Jaakko Fagerlund
10-14-2012, 05:09 AM
Carbide tools are convient but expensive.
Mainly depends what sort of inserts you use. I use DNMG inserts for 99% of my turning (OD and ID). They have 4 corners to use and cost me around 5-10 EUR per insert, so that makes around 1-2 EUR per corner. One other insert (can't remember the designation now) I have that my smallest boring bars use where the DNMG just doesn't fit in.

Makes it very cheap to use only a couple of different inserts and to have insert holders that use the same inserts.