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19th January 2014, 07:03 PM #1
4 x 6 Bandsaw wheel aduster block
Stupidly, I thought I was almost home and hosed in setting up my H&F BS4A Band saw.
Having obtained some Starret bi metal blades replacements for the busted standard one, I was able to get the saw cutting square in both planes . I always de tension the blade after use. I went to retension the blade this morning to do a cut and it there was a resounding crack followed by an inability to gain blade tension.
Oh,crap, I have snapped the blade I thought. Dis-assembly showed that the sliding adjustment block had snapped through the 16mm hole. Given the wheel spindle is 15mm diameter ,this hole serves as the the hinge point for the coplanar adjustment of the idler wheel.
The block measures 25.4 wide and has 16mm hole in its face and some 4 x 4 mm slots on the faces perpendicular to the 25.4mm wide face. There are also 2 other holes ,1 for the 8mm adjuster set screw and one clearance hole to anchor the tensioner spindle. That leaves some very thin cross section when you do the maths.
Obviously no has told the Chinese that while cast iron is great stuff under compression ,it it also exhibits poor strength under tension and shear forces, both which occur in the block under load.Zoom in on the cross section photo and you will see where the edge of the hole has been dressed.That alone makes for a stress point as a crack starter.
I don't think I have over tensioned it as I have not much strength now in my hands and wrists due to arthritic problems.
I will braze it up just to get me by, but in the long run ,I think I want to re -design the block as a steel unit to be stronger.It will be along the lines of a vertical band saw where the spindle is hinged and can only move vertically with adjustment but not laterally.
Somehow the the 16mm hole dimension seems a bit oversize to me ?
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19th January 2014, 10:53 PM #2SENIOR MEMBER
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That's pretty crappy quality Grahame, or penny pinching by the manufacturers.
On my Rong Fu that part is solid steel. Would be pretty easy to make one up out of steel - basic machining.
Also I hear that the vice nut is also cast and breaks real easy on those modern ones. That bit was missing on the Rong Fu so I don't know what it was made from, but I made one out of steel anyway.
Hope you get it up and running soon. I don't de-tension either of my bandsaws, and nothing evil has ever happened.
PS. my Bro in Law saw my cheap BS today, got overly excited, and now he wants one So I'm on the hunt for another one, whatever the brand, so long as it costs less than $150 and is in Adelaide.
Cheers
RobThe worst that can happen is you will fail.
But at least you tried.
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19th January 2014, 11:08 PM #3GOLD MEMBER
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19th January 2014, 11:50 PM #4
I've never heard that Stu, but then the saw i used to use was ancient and huge, a little bit of tension on the rubber would probably not have done squat on a 30" wheel.
Shame about the saw Grahame,
Just think you could have the fun of replacing worm gears or finding carbide pads instead....
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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20th January 2014, 08:58 AM #5GOLD MEMBER
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Maybe it's different with smaller home use bandsaws, but I can't imagine steel merchants or machine shops taking the time to slacken the saw blades in-between cuts or even at the end of each day for that matter. I certainly have no intention of giving mine any such moooshy treatment. It's had over 40 years of hard treatment, I worried if I start that sort of thing then next thing you know it will want to sleep inside at night!
Edit: Sorry to hear about the saw. It's never a nice sound to hear when you are tightening something up. Luckily it looks a rather simple part for someone like yourself to fix. The fix will no doubt be better than any original and will last the life of the saw!
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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20th January 2014, 04:20 PM #6SENIOR MEMBER
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It's interesting you should say that Grahame, as the same thought crossed my mind when I had it all apart to re-sleeve/bush the idler pulley.
Although steel, mine is the same in that the hole is definitely a couple of mm oversized, and I wondered at the time why they had done that, considering tolerances everywhere else are close.
It looks to me that it provides clearance for angular movement when you adjust the set screw to tilt the pulley mounting shaft.
The block that you broke remains parallel by the function of the two mounting strips that lock into each side of it, and only the shaft tilts in the hole.
RobThe worst that can happen is you will fail.
But at least you tried.
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23rd January 2014, 07:40 PM #7
Hi Stu,
The instruction on the MACC 400 ( my employers new eyetalian bandsaw) says to de tension the blade if the saw is to be left standing idle for any time. Given the correct blades for the work and run in and operated as per instruction it has not missed a beat. Our work structure is that for this machine, use is sporadic.
Like a hand held hacksaw it is possible to induce a curvature in the bow of the saw from the tension in the blade. Given that the cast iron used in this particular Chinese aberration, is probably only marginally stronger the recycled peanut paste, I am taking no chances with it.
Bugger it! I might as well go the whole hog and remove as many bugs as I can.
Changes I have made to date
A new stand, longer wider and higher.
A zeroing block to regain vice jaw square to blade after change back from a bevel cut.( Thanks Rob)
Adjusting threads changed over to tool free operation where possible.
A locking device to keep the bow frame down , when being wheeled about. Thanks again Rob)
A swarf tray
Small gutters to pick up the swarf that the tray misses.
A knurled knob for the blade sheet metal cover
A small amount of machining to allow the tension knob /washer to bear squarely against the bow frame surface
Changes to make
Clean out the gearbox and change to the correct oil. The wrong oil used here can eat into the bronze/brass worm wheel.Any know of a local equivalent gear oil to Mobil SC 634($300 per 20L) that's available in a liter bottle.?
A three arm tension wheel - the original knob is very difficult to tighten with my arthritic hands.
A coolant system
A hydraulic controlled down feed .
a super duper blade wiper for stripping off swarf before in gets to the drive wheel.
If I do a task or two every night who knows I may have a half decent saw before too long.
Grahame
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24th January 2014, 08:23 AM #8SENIOR MEMBER
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Sounds good Grahame.
How did you fix your broken block?
Another mod you may want to consider is an adjustable vise stop screw, for cutting very short lengths.
I think this is a necessary mod.
See my video below for how I did it.
My $85 4x6 metal bandsaw - restoration - YouTube
Cheers
RobThe worst that can happen is you will fail.
But at least you tried.
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24th January 2014, 10:09 AM #9GOLD MEMBER
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Good work Grahame.
Hi Rob,
I have watched a number of your videos but I have never made comment on them. Probably a good time to say that I really find them entertaining and educational. Thanks Rob!
Cheers,
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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24th January 2014, 12:34 PM #10SENIOR MEMBER
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Thanks Simon.
If no body chipped in, there wouldn't be much to see on the internet.
Cheers
RobThe worst that can happen is you will fail.
But at least you tried.
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24th January 2014, 05:01 PM #11
Rob,
The block has been prepped prior to welding.I have opted to tig it using MMAW stainless as a filler rod.
I have a pair of drop in blocks, both longer than the rear jaw, the front one being drilled and tapped with a rod and knurled knob.I can move them up to the blade and cut a millimeter off if I choose to.
For the moment I have put them down in a safe place and when I find them again will take a pic.
Grahame
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27th January 2014, 04:34 PM #12GOLD MEMBER
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Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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30th January 2014, 05:48 PM #13
The block is welded but I don't think it will hold the cast is a bit different to weld with tig and did not wet too well. I am making a steel block to a better stronger design.
For any one that interested in the new design, I have some 25.4mm cold rolled square , I will drill holes for the adjuster grub screw and the tensioner. The tilting mechanism is just a 6mm slot in the 25mm square, that takes a flat machined into the end of the 15mm diameter spindle.The flat spindle end will pivot on a M6 shoulder bolt. Only minimal side slop is possible, just up and down movement.It has to be stronger, there's lots more cross section and that is in steel not crap iron.
For anybody that is also chasing the gearbox oil oil for one of the the little sods, I found Penrite 85W-140 a mineral gear oil which Penrite say is OK for copper alloys, so obviously brass well. $14 and some change at Auto barn for a liter ,but the SuperCheap Auto also have it. Also Goggle the Penrite site for a list of sellers.
A question for you ,my machinist friends. I have a face plate for the 12 x 36 that i was going to mount the 180mm ( 7 3/8") bandsaw wheels on to bore and true the saw blade surfaces.
The band saw wheels are 3 legged and the lathe face plate has 8 x 15 wide slots, so the plan was was to screw the wheel to the plate , bolting the plate through 4 opposing slots and tap/slide it the whole shebang into alignment checking it with a dial.
Is this what a real machinist would do or is there a better way to go about the procedure?
thanks
Grahame
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31st January 2014, 07:12 AM #14SENIOR MEMBER
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Hi Grahame,
If it was me I would machine a plug that fits neatly in the hole in the faceplate and neatly into the bore of the bandsaw wheel.
This will help with true original alignment. Clamp the wheel in position then remove the plug out through the back of the faceplate (if possible) and you should be good to go.
This way the bore can be machined true to the outer diameter and vica verca.
Phil
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31st January 2014, 09:36 AM #15SENIOR MEMBER
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There should be enough metal in the pulley lip to mount it using the external jaw set in the 4 jaw chuck.
I considered doing this when looking at options to rebuild my idler pulley centre (I briefly thought about opening out the cetre of the pulley).
In regard to welding the cast, I would have definitely bronzed both sections seperately to get full penetration, rather than use TIG. Anyway steel sounds a lot better long term proposition. Be interesting to see photos of the new design.
Cheers
RobThe worst that can happen is you will fail.
But at least you tried.
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