4 files changed, +81 −14 1.1.0: Real tooth grooves. detail = simple keeps a plain cylinder.

part.py +45 −6

Copy diff

		@@ -1,9 +1,11 @@
1		-"""Flanged timing pulley, 2GT (GT2), 3GT (GT3) and MXL: envelope for assemblies.
	1	+"""Flanged timing pulley, 2GT (GT2), 3GT (GT3) and MXL. Axis along Z, the bottom flange's outer face on the XY plane; a flange of diameter F, 1 mm thick, at each end of the width W;
	2	+optionally the hub (diameter D, up to the overall length L) above the top flange. Set screws are not modelled.
2	3
3		-The toothed body is drawn at its outside diameter O.D. (teeth not modelled: only the tooth groove's depth is published),
4		-axis along Z, the bottom flange's outer face on the XY plane. A flange of diameter F, 1 mm thick, at each end of the
5		-width W; optionally the hub (diameter D, up to the overall length L) above the top flange. Set screws are not modelled.
	4	+detail = "full": the body at its outside diameter O.D. with its tooth grooves cut in. MXL grooves follow the published rack: depth 0.64, bottom 0.67, flanks 20 degrees (28 under 24 teeth).
	5	+2GT and 3GT publish the groove depth only, so the rounded groove's width is a proportion for looks, not for design. detail = "simple": a plain cylinder at O.D.
6	6	"""
	7	+import math
	8	+
7	9	from steve import Model
8	10
9	11	profile = "2GT" # Belt profile
		@@ -11,6 +13,7 @@
11	13	belt_width = 6 # mm Nominal belt width
12	14	bore = 5 # mm Bore
13	15	hub = False # Hub above the top flange (shape B)
	16	+detail = "full" # full: tooth grooves; simple: a plain cylinder at the outside diameter
14	17
15	18	# profile: {teeth: (P.D., O.D., D, F, E)}, D None: no hub offered. MISUMI FA Mechanical Components, High Torque Timing
16	19	# Pulleys 2GT pp. 1381-1382, 3GT pp. 1383-1384, Timing Pulleys MXL pp. 1389-1390 (2014), Number of Teeth / Dimension tables.
		@@ -58,9 +61,45 @@
58	61	if bore + 2 > e:
59	62	raise ValueError(f"Bore {bore} leaves no wall under the teeth: at most {e - 2} mm.")
60	63
	64	+# profile: groove depth, from the Standard Tooth Profile drawings of the same pages (2GT 0.75; 3GT 1.14; MXL 0.64).
	65	+GROOVE_DEPTH = {"2GT": 0.75, "3GT": 1.14, "MXL": 0.64}
	66	+PITCH = {"2GT": 2.0, "3GT": 3.0, "MXL": 2.032}
	67	+GROOVE_WIDTH = 0.62 # x pitch: mouth of the rounded 2GT and 3GT grooves, a proportion for looks
	68	+MXL_BOTTOM = 0.67 # bottom of the MXL groove, same pages
	69	+
	70	+if teeth not in PULLEYS[profile]:
	71	+ raise ValueError(f"{profile} tooth counts in the source: {', '.join(str(t) for t in PULLEYS[profile])}.")
	72	+if belt_width not in WIDTHS[profile]:
	73	+ raise ValueError(f"{profile} belt widths: {', '.join(str(w) for w in WIDTHS[profile])} mm.")
	74	+pd, od, d_hub, f, e = PULLEYS[profile][teeth]
	75	+a, w, l = WIDTHS[profile][belt_width]
	76	+if hub and d_hub is None:
	77	+ raise ValueError(f"{profile} {teeth} teeth: the source offers no hub for this size.")
	78	+if bore + 2 > e:
	79	+ raise ValueError(f"Bore {bore} leaves no wall under the teeth: at most {e - 2} mm.")
	80	+
61	81	model = Model()
62		-with model.sketch("body_sketch", on="XY", name="Toothed body") as sk:
63		- sk.circle("body_od", (0, 0), od / 2)
	82	+radius = od / 2
	83	+depth = GROOVE_DEPTH[profile]
	84	+if detail == "simple":
	85	+ with model.sketch("body_sketch", on="XY", name="Toothed body") as sk:
	86	+ sk.circle("body_od", (0, 0), radius)
	87	+else:
	88	+ if profile == "MXL":
	89	+ flank = math.tan(math.radians(28 if teeth < 24 else 20))
	90	+ half_bottom = MXL_BOTTOM / 2
	91	+ groove = [(half_bottom + depth * flank, 0.0), (half_bottom, depth), (-half_bottom, depth), (-half_bottom - depth * flank, 0.0)]
	92	+ else:
	93	+ half_mouth = GROOVE_WIDTH * PITCH[profile] / 2
	94	+ groove = [(half_mouth * math.cos(math.pi * i / 6), depth * math.sin(math.pi * i / 6)) for i in range(7)]
	95	+ outline = []
	96	+ for n in range(teeth):
	97	+ centre = 2 * math.pi * n / teeth
	98	+ for u, v in groove:
	99	+ angle = centre - u / radius
	100	+ outline.append(((radius - v) * math.sin(angle), (radius - v) * math.cos(angle)))
	101	+ with model.sketch("body_sketch", on="XY", name="Toothed body") as sk:
	102	+ sk.polyline("body_outline", outline, closed=True)
64	103	model.extrude("body", "body_sketch", distance=w, name="Toothed body")
65	104	with model.sketch("flange_low_sketch", on="XY", name="Lower flange") as sk:
66	105	sk.circle("flange_low_od", (0, 0), f / 2)

pypart.toml +10 −4

Copy diff

		@@ -1,12 +1,11 @@
1	1	name = "steve/timing-pulley"
2		-version = "1.0.0"
	2	+version = "1.1.0"
3	3	runtime = "steve"
4	4	license = "MIT"
5	5	summary = "Flanged timing pulley envelope: GT2 (2GT), GT3 (3GT) and MXL, tooth counts, belt widths and bores as presets."
6		-description = """Flanged timing pulley for 2GT, 3GT and MXL belts as an envelope for assemblies: the toothed body at its outside \
7		-diameter, two flanges and the bore, optionally with a hub. Teeth and set screws are not modelled. Axis along Z, bottom flange \
8		-on the XY plane. Dimensions from a maker's public catalogue (see the README); not affiliated with any maker or belt brand."""
	6	+description = """Flanged timing pulley for 2GT, 3GT and MXL belts: the toothed body with its grooves cut in, two flanges and the bore, optionally with a hub. Set screws are not modelled. detail = simple is a plain cylinder at the outside diameter for big assemblies. Axis along Z, bottom flange on the XY plane. Dimensions from a maker's public catalogue (see the README); not affiliated with any maker or belt brand."""
9	7	tags = ["pulley", "timing-pulley", "gt2", "gt3", "mxl", "belt", "power-transmission"]
	8	+changes = "Real tooth grooves. detail = simple keeps a plain cylinder."
10	9
11	10	[parameters.profile]
12	11	type = "choice"
		@@ -45,3 +44,10 @@
45	44	label = "Hub"
46	45	description = "Hub above the top flange (the source's shape B), on sizes that offer one."
47	46
	47	+[parameters.detail]
	48	+type = "choice"
	49	+default = "full"
	50	+choices = ["full", "simple"]
	51	+label = "Detail"
	52	+description = "full: tooth grooves. simple: a plain cylinder at the outside diameter, for big assemblies."
	53	+

presets.toml +21 −0

Copy diff

		@@ -1512,3 +1512,24 @@
1512	1512	aliases = ["MXL 40 tooth", "MXL 40T", "MXL pulley 40 tooth", "MXL 40T 10mm bore", "MXL 40 teeth bore 10", "MXL", "belt profile=MXL; teeth=40; bore=10 mm; belt width=6.35 mm; flanged"]
1513	1513	standard = "MISUMI catalogue"
1514	1514
	1515	+[[presets]]
	1516	+id = "GT2-20T-B5-W6-simple"
	1517	+title = "GT2 20 teeth, bore 5, belt 6 mm, simple (no grooves)"
	1518	+params = { profile = "2GT", teeth = 20, belt_width = 6, bore = 5, hub = false, detail = "simple" }
	1519	+aliases = ["GT2 20T simple"]
	1520	+standard = "MISUMI catalogue"
	1521	+
	1522	+[[presets]]
	1523	+id = "GT2-40T-B8-W6-hub"
	1524	+title = "GT2 40 teeth, bore 8, belt 6 mm, with hub"
	1525	+params = { profile = "2GT", teeth = 40, belt_width = 6, bore = 8, hub = true }
	1526	+aliases = ["GT2 40T hub"]
	1527	+standard = "MISUMI catalogue"
	1528	+
	1529	+[[presets]]
	1530	+id = "MXL-40T-B8-W6.4-hub"
	1531	+title = "MXL 40 teeth, bore 8, belt 6.4 mm, with hub"
	1532	+params = { profile = "MXL", teeth = 40, belt_width = 6.4, bore = 8, hub = true }
	1533	+aliases = ["MXL 40T hub"]
	1534	+standard = "MISUMI catalogue"
	1535	+

README.md +5 −4

Copy diff

		@@ -6,13 +6,13 @@
6	6
7	7	Axis along Z, bottom flange's outer face on the XY plane:
8	8
9		-- the toothed body, a cylinder at the **outside diameter O.D.** over the width **W**. Teeth aren't modelled: the source
10		- gives the tooth groove's depth, not its full shape, and it says the groove varies with the number of teeth;
	9	+- the toothed body at the **outside diameter O.D.** over the width **W**, with its grooves cut in;
11	10	- a flange of diameter **F**, 1 mm thick, at each end of W;
12	11	- the bore; with `hub`, a hub of diameter **D** up to the overall length **L**.
13	12
14		-The pitch diameter **P.D.** sits outside the O.D. and is in the table below, for centre distances. Set screws aren't
15		-modelled.
	13	+**MXL** grooves follow the published rack: depth 0.64, bottom 0.67, flanks 20° (28° under 24 teeth). **2GT and 3GT:** the source draws a rounded groove and dimensions its depth (0.75 and 1.14) only, adding that it varies with the number of teeth, so the groove's width is a proportion for looks, not for design.
	14	+
	15	+The pitch diameter **P.D.** sits outside the O.D. and is in `part.py`, for centre distances. `detail = "simple"` is a plain cylinder at O.D., for big assemblies. Set screws aren't modelled.
16	16
17	17	## Parameters
18	18
		@@ -23,6 +23,7 @@
23	23	| `belt_width` | Nominal belt width: 2GT 6, 9; 3GT 6, 9, 15; MXL 4.8, 6.4, 9.5, 12.7 |
24	24	| `bore` | Bore, mm |
25	25	| `hub` | Hub above the top flange, on sizes that offer one |
	26	+| `detail` | `full` (tooth grooves) or `simple` (plain cylinder at O.D.) |
26	27
27	28	## Source
28	29