Bit speed for hollow square mortice chisel
71Atlas
| Posted in General Discussion on
My problem is with my hollow square mortice chisel bit. After setting the correct space between the bit and the chisel (thickness of a dime) and drilling 2 or 3 holes the bit begins to extend out of the drill chuch and becomes very hard to cut deeper. I am cutting a 1/4′” square mortice hole and the bit shank is 0.170 dia. and the spindle speed is 350 rpm. This is the second hollow chisel, the first chisel was low cost but the new one is a pricey Japanese make but both are doing the same thing, the bit pulls out of the drill chuck. What should the drill bit speed be for 1/4″ hollow mortice chisel? Are there any rules for various size holes as to what speed for the drill bit?
Replies
71Atlas,
I assume you use a drill press and not a hollow chisel mortiser because I do not think that any hollow chisel mortiser would run at such a low speed. I do not think your problem has anything to do with the speed of the machine but I think that the drill press is not properly aligned, that is, the quail of the drill press is not perfectly square to the table. If the chisel goes in the stock at a slight angle, the chisel gets stuck after penetrating a small distance. The fact that you used a different chisel and the problem persisted is a clue that the problem is with the machine.
Aurel Ionica
Is the bit extending more from the chuck or is the chisel housing being pushed further up the quill?
Are you tightening the bit using all three holes in the chuch?
My dedicated morticer (Powermatic 719) runs at 1720 RPM. For such a small bit, 350 seems awfully low.
7,
I think that the speed you are running is much too slow- even three times that speed wouldn't be too slow, as 1/4 is a small mortice, so try speeding it up.
Mortisers that rely on (I assume) a drill chuck are not good, especially if it is a diy type chuck. You should at least tighten one of those at all three positions, even go round again.
My Multico runs at 2800rpm, which is on the fast side I feel, especially for bigger mortices.
You mention a speed of 350 rpm. This got me to thinking - Did you leave out a 4? Common speeds of of mortisers are 3450 or 1725 rpm. It sounds like you either don't have the bit or the chisel tight enough to keep them from slipping.
I have just finished a job for the trestle of my work bench. I made eight mortises of 2 X 3 by 2 inches deep with repeated plunges with a 1/2 inch chisel. I have the PM 719 and noticed that sometimes it was hard to pull the chisel out from the depth of the wood. I finally put on an extra clamp to hold the wood in place.
If you find the chisel hard to withdraw measure it at top and bottom: good quality chisels are ground slightly wider at the cutting end, to avoid this problem.
Re speeds: I note that Multico make a two speed version of their big model machine- 1450 and 2850 rpm European electrics. This is far more practical .
I would post a picture but it is too much fuss now with the new system
71Atlas
I high speed for a hollow mortice chisel is not a plus but a minus because it wears the chisel and the bit excessively. I got rid of my hollow chisel mortiser and I use a drill press because I have control over the speed and can run it at around 500 rpm. For such a small chisel you do not need to use a lot of force to tighten the chuck or to press the chisel into the stock because the chisel can crack and the bit can break. Such a small chisel should go in hard wood like oak pretty easy even after you make the first hole and should also come out pretty easy. As I said, check the alignment of the machine and make sure that the yoke that attaches the chisel to the drill press quail is properly centered with the chuck. Tools are designed to work smooth and when you force them or over tighten them you are abusing them.
Aurel Ionica
I adjusted the speed to 1700 RPM and what do you know, it worked great. DUH
Just read your original post Atlas. I did a test with various size forstner bits (1/4'- 1 5/8") about a year ago. The smaller bits work best in the range from 1250 to 2000 rpm. When you get to the larger bits over 1" you have to slow them down to get them to be efficient.
And when I say slow them down.. I found that 1 1/2" bits were most effective from 650 to 750 rpm. The bottom line is that even larger bits don't fare as well below 600 rpm and what you originally did was much to slow as you found out. 350 rpm is really more in the range for drilling metal. I cannot comment on large 4" to 6" fly bits as I don't use them on a drill press as there are better options IMO.
Glad to see you on track here. BTW.. I have a 650 pound industrial floor mortiser. If you ever break or dis-temper a hollow mortise chisel it will most likely be your 1/4" as it is the trickest to find a plunge speed (feed speed if you will) so don't be shocked if it were to happen. I have never dis-tempered a HMC larger than that and I work pretty exclusively with hard-wood and on a daily basis.
Sarge,
Don't tell 71Atlas
Sarge,
Don’t tell 71Atlas that a lower speed might work because he believed that the speed was the problem from the beginning and instead of trying a higher speed he posted the question here and after that he said that he was right and we do not know what we are talking about. I use regularly a 5/16" chisel (a little larger than 1/4") and goes in mahogany like in butter even at 200 rpm, which is the lowest speed on my drill press. Of course, I aligned my press with a test dial indicator like you aline the head of a milling machine. What people do not realize is that when the drill bit of a mortising chisel spins so fast in hard wood clogged with chips with very narrow passages to eject, they heat up so fast that they get blued, loose their temper and the chisel cracks. But what do woodworkers know about machines? All they know is crank up the speed and bring more muscles. DUH.
Aurel Ionica
My "big boy" floor mortiser operates at a constant speed of 1720 so I have no alternatives to speed change Aurel. But.. even though a lower speed will work on my drill press with 1/4" forstners.. I looked for the best speed to run small and large bits to avoid changing speeds constantly even though that is fairly easy. By using a plunge and release just before the chips begin to clog.. along with the tip of a shop vac hose mounted just over the top of the forstner bit on the hollow chisel... that speed was around 700 rpm.
At this point I just leave my drill press set on that speed as I mainly cut mortises on it but do drill some standard holes. The only time I change that is when I take metal to the machine. And yes.. allowance for chip ejection is important to avoid dis-temper and slowing down the process.. very important.
Regards...
Sarge,
I realized that I was talking to someone who has experience with mortising hollow chisels. You did mention that you made some tests with different size bits and different speeds, but the speeds at which you can run cutting tools in different materials, including different kinds of wood is given in books like Machinery’s Handbook. In these books, they give you the speed in feet/min. and not in rpm. because the speed of a cutting edge of a drill bit is calculated by calculating the circumference of the cutter based on the diameter and multiplied with de rpm. Consequently, they would tell you what you found out experimentally, that is, a larger bit would have to slowed down because the speed of the cutting edge is greater on a larger bit than on a smaller bit. In other words, if your run a smaller bit at a higher rpm. the speed of the cutting edge could be the same as the one of a large bit at a lower rpm. A machinist would now that any tool would cut better at a lower speed because the heat builds at the cutting edge and the lower the speed the cooler the bit is, but the cut would take longer therefore books never indicate the lowest speed at which you can run a bit but the highest so that you can make the cut as fast as possibly without ruining the bit because of the heat. As I said, I gave away a mortising machine because it did not have a variable speed and I use my drill press which has 15 speeds. In this way, I can increase the speed until the bit heats up but I do not have to wait between cuts for the bit to cool down. We should keep in mind that the problem of 71Atlas was that the mortice would get stuck and the bit would slip in the chuck. He did not say that he checked the squareness of his press (if indeed he uses a press as I suppose) or that he has ever checked it and that I was wrong, which does not surprise me about woodworkers. What he does not realize is that if his machine is not square and the chisel binds in the cut, as he forces it eventually it flexes and deflects, particularly taking into account that is such a flimsy chisel. Even if he can make the cuts, the walls of the mortices are not square and are uneven, which defeats the purpose of using the chisels. You did not say which wood did you use when you tested different speeds for chisels, but if a chisel works OK without overheating in pine, at the same speed in oak or hard maple can become a piece of junk after just several mortices. But let’s let 71Atlas find out himself by ruining his expensive Japanese chisel.
Aurel Ionica
Aurel
Put your thinking cap on a moment and look at this. It does not matter if the table is square to the quill of the press. That will not create a binding problem because the workpeice and/or table is not moving. If it did how would you cut an angled mortice as are sometimes used in chairs, not to mention other applications? Would this mean that angled mortices can only be hand cut? Someone forgot to tell that to the furniture companies.;o)
What does matter is that the drill bit, the chisel and the quill all be coaxial. (The sides or the chisel must be parallel to the direction of travel of the quill.) Milling machine tables are swept with an indicator to establish squareness so that when using large dia cutters they leave the workpeice parallel and unscalloped. Cutting a mortice at an angle is no different to the machine than just drilling a hole at an angle. If the drill bit is dull or improperly sharpened it could wander upon entry and cause deflection which could cause binding, but that is a different issue.
Rich
trialnut
You are partially right, but I pointed out that there are two problems: the quill being square to the table AND the joke that attaches the chisel to the quill to be properly centered with the chuck. I told 71Atlas to check BOUTH, because both can contribute to the problem. Although you are right that in theory, if the chisel is centered on the chuck it could go into stock at an angle, the fact is that any drill bit would wander when entering stock, and more so if it goes at an angle, and once the hole is started off center, it goes worse as it goes deeper. I know you may think that the spurs of the chisel would prevent the chisel from starting off center, but keep in mind that the bit starts first and the chisel penetrates the stock later. Moreover, a drill bit for a hollow chisel is asymmetrical because it only has one cutting spur (unlike a Forstner bit, for instance or a twisted drill bit) and its tendency to wander is greater. You may be right that you might be able to cut a square hole with a larger chisel when a chisel enters the stock at an angle, but I would not try that with a 1/4" chisel. Even when a press is squared by sweeping it with a test dial indicator, when drilling in metal, a hole must be started with a center drill for the drill bit not to wander, but that is not an option for using hollow square mortising chisels. Let’s not forget that the issue here is the chisel getting stuck in the wood and the bit slipping in the chuck, and I hope you agree that that should have nothing to do with the speed of the bit. If the chisel did work at a higher speed, I would explain that by the fact that at a higher speed the bit took shallower cuts when entering the stock and therefore wandered less, but this does not address the problem. Even if the drill press is properly squared and the chisel centered on the chuck, with such a small chisel I would start the hole very slowly and I would apply more pressure only after the spurs of the chisel sink in the wood and even then I would watch to see whether the chisel deflects or not. I wish someone had explained all these to me before I ruined two CLICO chisels.
Whew. I'm glad to now know
Whew. I'm glad to now know that a process that has been used by myself and others for many years does not work. How was it done??? Must have been smoke and mirrors. Extra Extra, read all about it. Angled mortices can only be cut by hand. Machining them is an illusion. :O
I believe the OP came back and said he upped his speed and the problem went away. Whats with that? More magic. There is an optimum speed for any cutting operation.
FYem,
" the issue here is the chisel getting stuck in the wood and the bit slipping in the chuck, and I hope you agree that that should have nothing to do with the speed of the bit."
A 1/4" mortising bit and chisel is prone to clogging and jamming, due, I believe to the shallowness of the bit's flutes. If they were deeper, there would be more room for the chips to be ejected, but then the bit itself would be too weak to resist the stresses of drilling. A low rpm exacerbates the clogging problem because the chisel can be forced into the wood faster than the bit can eject the chips thru those shallow flutes, and causes a traffic jam inside the chisel. A faster speed helps with this problem as, at the same feed rate, the bit in effect is taking smaller bites at each revolution. Faster bit speed= smaller chips= less clogging. Less tightly packed chips= less tendency for the bit to jam inside the chisel.
Of course, the faster the bit spins, when it does clog, the more likely it is to overheat, the heated chisel expands, and wedges itself in the cut... With a 1/4" bit and chisel, governing bit speed and feed rate is like walking a tightrope. Add a resinous wood, and it just gets worse. There's a reason they don't make 1/8" mortising chisels for the drill press.
Ray
I do believe I have to agree with what you said Ray. Keep in mind that my test was done in both hard-wood and soft-wood as I wanted to compare speeds so in reality it has little to do with mortising really. The Forstners has twin flutes.. the drill bit in a HMC has a single. The Forstners did not have to deal with a chisel housing surrounding them and the HMC has one.
I use 1/4".. 5/16".. 3/8".. 1/2" and 3/4" HMC often. I find that the smaller the bit the easier it is to clog the chips and that is where you have to observe and develope a feel for how deep to plunge and release to allow the chips to clear.
Also.. I owned a Shop Fox bench mortiser before I purchased the large floor model. It ran at 3450 rpm and you had to be especially careful with the chisels on that machine as the machine is very sturdy and has a long handle as a floor mortiser that has some hefty plunge ability.
If you plunged fast with smaller chisels on it at that speed and especially in hard-wood.. the chisel would over-heat and stick in the wood. I never gave any thought to the fact that it might be expanding as you mentioned but I did acutually break a 1/4" chisel on that machine so that theory sounds logical when I do think about it.
But.. regardless of the set speeds on both that machine (3450) and my current one (1720 I believe) I observed and experimented in scrap with the cheap stock chisels to find the best plunge and release rate to clear chips. Only after I got the floor model.. went through the learning curve on it did I move up to a set of more expensive chisels up to 1 1/2" which my machine can handle.
Just as a BTW.. anyone that think that either a cheap or expensive chisel comes sharp out of the box, I would have to dis-agree. IMO all of them improve with removing any machine marks and honing. They will still cut out of the box but.. not the way they will cut after you touch them up to operate at peak of what they are actually capable of doing.
Sarge,
I'm glad you and I are
Sarge,
I'm glad you and I are in agreement. As my grandma used to say,"Great minds run in the same channel." Or was that, "Fools think alike"??
Take it easy,
Ray
joinerswork,
I agree that chip ejection is the critical issue for a small chisel but I do not think that a high speed is necessarily the solution for chip ejection as long as you admit that a high speed increases the risk of building heat rapidly when the chisel clogs. Instead of increasing the speed, I argue for decreasing the feed. When the bit takes thinner shavings, they can be ejected more easily and if the speed is not very high, even when the chisel does clog, the heat does not build as much to ruin it. I think the problem with those who use hollow mortising chisels is that they tend to feed them at the same rate as they would feed a regular drill bit for the same rpm. and they do not realize that a bit for a mortising chisel has only one cutter and therefore, at the same feed and the same rpm. makes chips twice as thick as a twist drill bit or a Fortsner bit. Thick chips are much more difficult to push through the flutes of a small chisel. Another rule machinists have for drilling is that you never go in one pass more than twice the diameter of the bit without taking it out to clear the chips. I use the same rule for mortising chisels and for drilling wood. My policy is to control chip ejection by feed and not by speed, because a higher speed can also favor clogging because of the heat and resin build up.
Sarge,
I agree with you about sharpening new chisels. I actually lap the outside faces until they have a mirror finish and I sharpen also the inside bevel just as you sharpen a new bench chisel. The chisel not only cuts cleaner, but without the milling marks, it slides more easily in and out of the stock.
trialnut,
“Whew. I'm glad to now know that a process that has been used by myself and others for many years does not work.”
It clearly does not work for 71Atlas. Why don’t you explain to him why his chisel does not work? Machinists do not believe in magic as woodworkers do. They think that what they do is science and they must understand what they are doing and why something does not work. I learned more about my woodworking tools by reading introductory books for machinists than I learned from any woodworking books and magazines.
"It clearly does not work for 71Atlas."
He said it did after he changed the speed
"I learned more about my woodworking tools by reading introductory books for machinists than I learned from any woodworking books and magazines."
Oh No, shucky poo darn, (shuffles away head down, tail tucked and wimpering) I has been outranked!
I did not intend to start a spitten contest, only wanted to point out what was not the cause of the problem. I'm not into bantering so I'm done with this thread. Going back to my cage now to lurk and wait for my next victum to pounce on. :^)
Rich
trialnut
"I did not intend to
trialnut
“I did not intend to start a spitten contest, only wanted to point out what was not the cause of the problem. “
So you know that if you run a 1/4" hollow mortising chisel at a speed lower than 1750 rpm. it gets stuck after penetrating ½" and the bit slips in the chuck? You said you’ve been using these chisels for years. Have you tried to run one at a lower speed and found out that you ran into that problem? How come that I am able to run them at a much lower speed and I do not have the problem? How come that Sarge was able not only to run them at a lower speed, but found out that ½" chisels should be run at a lower speed for better results? Anyone who knows mortising machines knows that most of them run at 3500 rpm. and it is hard to find one that runs at 1750 rpm. and people look for ones that run at 1750 because the high speed is a problem. You display the kind of logic that most woodworkers have adopted and discussions never get anywhere because even when 71Atlas posted a question here, he already knew the answer. I ended up looking on this forum because I asked a common sense question at FW and after a long time they suggested to post it here because there are experienced woodworkers who might have an answer to it but I discover that I have wasted my time and this is what I should have known that discussing with woodworkers is just a waste of time. I will not waste my time on this forum anymore.
Be sure you are advancing the chisel in small bites. Drill and retract the chisel every 1/8" - 1/4".
In the shop I used to be involved with we had a big commercial mortiser. As I recall for chisels up to 3/8" will used about 600 rpm. For larger we used somewhat less--maybe 400 rpm.
Key to being able to mortise harder woods is to hone the outside four surfaces of your chisel to the same extent as you would for your bench chisels. In other words, use you stones to hone the surfaces to a high polish. This is even more important than honing the inside of the chisel cutting surface.
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