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11-09-2010, 07:04 PM #1
Sawmaster power hacksaw - do they all buck like this?
I recently ran into a Miller Knuth 3167 Sawmaster power hacksaw. It must be an early one as it does not have the power switch positioned to turn off at the end of a cut. The power switch is mounted to the front leg casting under the vise handle.
After a bit of cleanup I installed a new Starrett 14x1 10tpi hack saw blade and tried cutting a piece of 1" angle iron. The saw cuts well but bucks upward as it relieves the spring pressure at the end of each cutting stroke. Now the Sawmaster is a bit different than other power hacksaws as it spring loads the hacksaw down on the cutting stroke and relieves some of the spring load with cam action on the back stroke. It does not actually lift the blade on the back stroke. Is this normal?
Also, an thoughts on oil should I used? The on-line manual is not specific regarding viscosity (such as would 30 weight non-detergent work?) But in certain areas they do want an oil with adhesives.
11-10-2010, 10:26 AM #2
1) Thank you for posting nice photos of an interesting machine.
2) A 10 tpi blade might be a little bit too coarse for 1" angle, depending on whether it is light or heavy gauge angle. You should have minimum three or better yet four teeth fully within the thickness of the steel. You might be seeing an effect of the teeth catching in the work.
Try finer-pitch blades and see what happens.
3) I've had no luck with auto engine oils, including non-detergent oils, on machines that have wool felt oil wicks. It somehow clogs up the wicks.
An "oil with adhesives" sounds like Way Oil to me, but that's more of a guess than anything. I would presume this is on the sliding surfaces?
I hope others who know more about lubrication science chime in on this. We have at least one lubrication professional on PM. I hope he sees this.
11-10-2010, 12:28 PM #3
Many of the ones I have seen were either bolted to the floor or mounted on a hvy skid with rubber pads to prevent the saw from walking across the floor.
I assume you can reduce the spring tension to match the load. Is there a hand wheel for that? Should be.
Being a home hack I have no idea about proper lubrication. I got a deal on a 5 gallon can of 30wt non detergent and I use that for everything. When I finish this can, I think I will have a collectors item.
11-10-2010, 12:44 PM #4
Is the motor going round the right way?.......... don't laugh it can make a lot of difference on some of the more, shall we say, basic power hacksaws.
11-10-2010, 03:23 PM #5
Limy, That makes me think, maybe it would help to slow it down.
11-10-2010, 05:06 PM #6
Thanks for the replies. I did verify that the motor is turning the correct direction (counter clockwise when facing the open drive gear). But, on closer observation the previous owner must have been running it with the pitman arm not bolted to the large gear securely, since the original threaded how is stripped out. There are other threaded holes adjacent to this hole (before and after) but in either position there still seems to be the bucking. The previous owner also replaced the pitman arm with a much nicer designed home made one with an extra degree of freedom to minimize any alignment issues.
Lowering or raising the tension on the spring did not seem to make much difference. I did
have to put more tension on the included V belt than I would like to keep from slipping at the start of a cut. (per the manual I start with the blade not resting on the material).
Sounds like possible improvements are:
1) Use a 14 tpi blade (which is what the manual calls out for general use). Victor Machinery Exchange is one of the few places that has 14tpi and they are pretty cheap, but the brand is unknown (see link below).
2) Slow it down with a smaller motor pulley.
3 ) Change the motor to allow for variable speed. I could put a variable speed 1/3hp DC motor on it out of the junk pile. Or maybe that odd dual speed (1725/1140rpm) 1/3hp single phase motor I have had laying around.
4) Replace the V belt
5) Helicoil the original pitman arm mounting point on the big gear and see if the bucking in a spring tension lift-off timing issue.
I'll probably start with 1,2, & 4.
The Sawmaster is a 2x bigger and beefier hacksaw compared to the Craftsman/Cove/Atlas hacksaw I have used in the past. It would be interesting to see if for general once-off use which is more effective and easy to use. I like the handle on the front of the Sawmaster to engage the bigger blade, but the Craftsman has positive liftoff of the blade on the backstroke.
Thanks for the input.
Link to blades:
Power Hacksaw Blades - High Speed Steel - 12 to 24 inch long.
11-10-2010, 06:15 PM #7
That's a unique saw. I've been using a #6 Marvel for a little while now, long enough to get the hang of what it does effectively and what it's limitations are. While the saw I have is quite a bit larger it doesn't buck, vibrate or walk anywhere even with a full capacity cut in high gear where the moving components become a blurr. Coarse tooth blades in the thinest material haven't been a problem. I've cut 10 gauge steel with a 6 tpi blade. The cut was pretty good, no bucking or unusual issues, I was surprised it was as smooth under such use.
I use vactra 2 on the ways/pivots and DTE heavy medium in the bearings.
11-11-2010, 04:10 PM #8
What is that vertical handle at the back? Mine doesn't have that....
11-11-2010, 04:43 PM #9
I'm not harping on, but is the motor rotation as per manual?
I'd check up on stroke rates before altering the speed.
11-13-2010, 07:26 AM #10
the gizmo with the handwheel sticking up at the back end looks a lot like the feed adjuster on a marvel drawcut saw.If the manual that is available for your saw is not too great,you may get some insight from looking at some marvel manuals.
11-17-2010, 09:45 PM #11
k3vyl - the gizmo with the handwheel sticking up at the back end is the tension spring adjustment for the downward cutting force.
Limy Sami - I checked the motor rotation, it is the correct direction per the manual. I also unloaded the tension spring (effectively eliminating the downward spring force and making any timing issue of the cam moot). It still behaves the same.
RickWG - The vertical handle in the back is to pull the saw with (works better when there are wheels on the saw). Mine has part of the handle broken.
Garwood: I am envious of your marvel being able to cut light weight stuff. This one really cuts, but the downward force is large enough that it really wants to cut big stuff. For fun I put a piece of .093 x 2" aluminum on it and the saw cut half way thru before bending the aluminum in half. It makes me wonder if I should be adding a compression spring to reduce the downward force. I'll have to get a scale and measure the minimum downward force.
11-18-2010, 06:55 PM #12
If your saw doesn't have a means to positively limit downfeed I can't see it working very effectively on thinner materials regardless of blade tooth size. Are you certain the saw has no type of friction feed or downfeed limiting system that isn't working properly (I have no experience with saws like yours)
11-18-2010, 08:35 PM #13
I wonder what smaller sized power hacksaws exist with positive or friction feed?
I think a compression spring or gas strut to counteract the downward force (about 35 lbs on the blade at the minimum spring tension) for thinner material may be a simple solution. Or maybe just an adjustable hydraulic dashpot as seen on most horizontal bandsaws (like old Kalamazoo's) might work.
11-19-2010, 03:24 AM #14
You can always put light stock in a vise and use a hand saw or a sawzall. You really appreciate these heavy floor models on stuff like 2 inch bar stock.
The best tool for medium and light cutting are the small ban saws. In fact most home shops use the little 6 inch band saws. They are ideal for your needs. Perfect really.
Here is a link to what I mean. I DEFINITELY do not endorse this brand (not one way or other). FYI, this is the right type of tool for your job:
Horizontal/Vertical Metal Cutting Bandsaw
11-19-2010, 05:48 AM #15
peter - I agree, these saws are optimal for cutting thick stock.
After thinking about it last night, 35 lbs. of force on the blade seemed a bit excessive. So I rigged a tension spring to the end of the saw to counteract the weight and for fun tried cutting the same piece of thin aluminum with 7 pounds of cutting force. It cut the aluminum with no problem, though not quite as fast as with the higher cutting force. It also did not buck nearly as much.
11-19-2010, 05:34 PM #16
You may have addressed this but I didn't see which way you put the blade in. My marvel# 2 is definitely a drag saw and will jump off the floor if used the wrong way